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MKSH(1) 			   BSD General Commands Manual				  MKSH(1)

     mksh, sh -- MirBSD Korn shell

     mksh [-+abCefhiklmnprUuvXx] [-T /dev/ttyCn | -] [-+o option] [-c string | -s | file
	  [argument ...]]
     builtin-name [argument ...]

     mksh is a command interpreter intended for both interactive and shell script use.	Its com-
     mand language is a superset of the sh(C) shell language and largely compatible to the origi-
     nal Korn shell.

   I'm an Android user, so what's mksh?
     mksh is a UNIX shell / command interpreter, similar to COMMAND.COM or CMD.EXE, which has
     been included with Android Open Source Project for a while now.  Basically, it's a program
     that runs in a terminal (console window), takes user input and runs commands or scripts,
     which it can also be asked to do by other programs, even in the background.  Any privilege
     pop-ups you might be encountering are thus not mksh issues but questions by some other pro-
     gram utilising it.

     Most builtins can be called directly, for example if a link points from its name to the
     shell; not all make sense, have been tested or work at all though.

     The options are as follows:

     -c string	mksh will execute the command(s) contained in string.

     -i 	Interactive shell.  A shell is ``interactive'' if this option is used or if both
		standard input and standard error are attached to a tty(4).  An interactive shell
		has job control enabled, ignores the SIGINT, SIGQUIT, and SIGTERM signals, and
		prints prompts before reading input (see the PS1 and PS2 parameters).  It also
		processes the ENV parameter or the mkshrc file (see below).  For non-interactive
		shells, the trackall option is on by default (see the set command below).

     -l 	Login shell.  If the basename the shell is called with (i.e. argv[0]) starts with
		'-' or if this option is used, the shell is assumed to be a login shell; see
		Startup files below.

     -p 	Privileged shell.  A shell is ``privileged'' if this option is used or if the
		real user ID or group ID does not match the effective user ID or group ID (see
		getuid(2) and getgid(2)).  Clearing the privileged option causes the shell to set
		its effective user ID (group ID) to its real user ID (group ID).  For further
		implications, see Startup files.

     -r 	Restricted shell.  A shell is ``restricted'' if this option is used.  The follow-
		ing restrictions come into effect after the shell processes any profile and ENV

		o   The cd (and chdir) command is disabled.
		o   The SHELL, ENV, and PATH parameters cannot be changed.
		o   Command names can't be specified with absolute or relative paths.
		o   The -p option of the built-in command command can't be used.
		o   Redirections that create files can't be used (i.e. '>', '>|', '>>', '<>').

     -s 	The shell reads commands from standard input; all non-option arguments are posi-
		tional parameters.

     -T tty	Spawn mksh on the tty(4) device given.	Superuser only.  If tty is a dash, detach
		from controlling terminal (daemonise) instead.

     In addition to the above, the options described in the set built-in command can also be used
     on the command line: both [-+abCefhkmnuvXx] and [-+o option] can be used for single letter
     or long options, respectively.

     If neither the -c nor the -s option is specified, the first non-option argument specifies
     the name of a file the shell reads commands from.	If there are no non-option arguments, the
     shell reads commands from the standard input.  The name of the shell (i.e. the contents of
     $0) is determined as follows: if the -c option is used and there is a non-option argument,
     it is used as the name; if commands are being read from a file, the file is used as the
     name; otherwise, the basename the shell was called with (i.e. argv[0]) is used.

     The exit status of the shell is 127 if the command file specified on the command line could
     not be opened, or non-zero if a fatal syntax error occurred during the execution of a
     script.  In the absence of fatal errors, the exit status is that of the last command exe-
     cuted, or zero, if no command is executed.

   Startup files
     For the actual location of these files, see FILES.  A login shell processes the system pro-
     file first.  A privileged shell then processes the suid profile.  A non-privileged login
     shell processes the user profile next.  A non-privileged interactive shell checks the value
     of the ENV parameter after subjecting it to parameter, command, arithmetic and tilde ('~')
     substitution; if unset or empty, the user mkshrc profile is processed; otherwise, if a file
     whose name is the substitution result exists, it is processed; non-existence is silently

   Command syntax
     The shell begins parsing its input by removing any backslash-newline combinations, then
     breaking it into words.  Words (which are sequences of characters) are delimited by unquoted
     whitespace characters (space, tab, and newline) or meta-characters ('<', '>', '|', ';', '(',
     ')', and '&').  Aside from delimiting words, spaces and tabs are ignored, while newlines
     usually delimit commands.	The meta-characters are used in building the following tokens:
     '<', '<&', '<<', '<<<', '>', '>&', '>>', '&>', etc. are used to specify redirections (see
     Input/output redirection below); '|' is used to create pipelines; '|&' is used to create co-
     processes (see Co-processes below); ';' is used to separate commands; '&' is used to create
     asynchronous pipelines; '&&' and '||' are used to specify conditional execution; ';;', ';&'
     and ';|' are used in case statements; '(( .. ))' is used in arithmetic expressions; and
     lastly, '( .. )' is used to create subshells.

     Whitespace and meta-characters can be quoted individually using a backslash ('\'), or in
     groups using double ('"') or single (''') quotes.	Note that the following characters are
     also treated specially by the shell and must be quoted if they are to represent themselves:
     '\', '"', ''', '#', '$', '`', '~', '{', '}', '*', '?', and '['.  The first three of these
     are the above mentioned quoting characters (see Quoting below); '#', if used at the begin-
     ning of a word, introduces a comment - everything after the '#' up to the nearest newline is
     ignored; '$' is used to introduce parameter, command, and arithmetic substitutions (see
     Substitution below); '`' introduces an old-style command substitution (see Substitution
     below); '~' begins a directory expansion (see Tilde expansion below); '{' and '}' delimit
     csh(1)-style alterations (see Brace expansion below); and finally, '*', '?', and '[' are
     used in file name generation (see File name patterns below).

     As words and tokens are parsed, the shell builds commands, of which there are two basic
     types: simple-commands, typically programmes that are executed, and compound-commands, such
     as for and if statements, grouping constructs, and function definitions.

     A simple-command consists of some combination of parameter assignments (see Parameters
     below), input/output redirections (see Input/output redirections below), and command words;
     the only restriction is that parameter assignments come before any command words.	The com-
     mand words, if any, define the command that is to be executed and its arguments.  The com-
     mand may be a shell built-in command, a function, or an external command (i.e. a separate
     executable file that is located using the PATH parameter; see Command execution below).
     Note that all command constructs have an exit status: for external commands, this is related
     to the status returned by wait(2) (if the command could not be found, the exit status is
     127; if it could not be executed, the exit status is 126); the exit status of other command
     constructs (built-in commands, functions, compound-commands, pipelines, lists, etc.) are all
     well-defined and are described where the construct is described.  The exit status of a com-
     mand consisting only of parameter assignments is that of the last command substitution per-
     formed during the parameter assignment or 0 if there were no command substitutions.

     Commands can be chained together using the '|' token to form pipelines, in which the stan-
     dard output of each command but the last is piped (see pipe(2)) to the standard input of the
     following command.  The exit status of a pipeline is that of its last command, unless the
     pipefail option is set (see there).  All commands of a pipeline are executed in separate
     subshells; this is allowed by POSIX but differs from both variants of AT&T UNIX ksh, where
     all but the last command were executed in subshells; see the read builtin's description for
     implications and workarounds.  A pipeline may be prefixed by the '!' reserved word which
     causes the exit status of the pipeline to be logically complemented: if the original status
     was 0, the complemented status will be 1; if the original status was not 0, the complemented
     status will be 0.

     Lists of commands can be created by separating pipelines by any of the following tokens:
     '&&', '||', '&', '|&', and ';'.  The first two are for conditional execution: ``cmd1 &&
     cmd2'' executes cmd2 only if the exit status of cmd1 is zero; '||' is the opposite - cmd2 is
     executed only if the exit status of cmd1 is non-zero.  '&&' and '||' have equal precedence
     which is higher than that of '&', '|&', and ';', which also have equal precedence.  Note
     that the '&&' and '||' operators are "left-associative".  For example, both of these com-
     mands will print only "bar":

	   $ false && echo foo || echo bar
	   $ true || echo foo && echo bar

     The '&' token causes the preceding command to be executed asynchronously; that is, the shell
     starts the command but does not wait for it to complete (the shell does keep track of the
     status of asynchronous commands; see Job control below).  When an asynchronous command is
     started when job control is disabled (i.e. in most scripts), the command is started with
     signals SIGINT and SIGQUIT ignored and with input redirected from /dev/null (however, redi-
     rections specified in the asynchronous command have precedence).  The '|&' operator starts a
     co-process which is a special kind of asynchronous process (see Co-processes below).  Note
     that a command must follow the '&&' and '||' operators, while it need not follow '&', '|&',
     or ';'.  The exit status of a list is that of the last command executed, with the exception
     of asynchronous lists, for which the exit status is 0.

     Compound commands are created using the following reserved words.	These words are only
     recognised if they are unquoted and if they are used as the first word of a command (i.e.
     they can't be preceded by parameter assignments or redirections):

	   case     else     function	  then	    !	    (
	   do	    esac     if 	  time	    [[	    ((
	   done     fi	     in 	  until     {
	   elif     for      select	  while     }

     In the following compound command descriptions, command lists (denoted as list) that are
     followed by reserved words must end with a semicolon, a newline, or a (syntactically cor-
     rect) reserved word.  For example, the following are all valid:

	   $ { echo foo; echo bar; }
	   $ { echo foo; echo bar<newline>}
	   $ { { echo foo; echo bar; } }

     This is not valid:

	   $ { echo foo; echo bar }

	   Execute list in a subshell.	There is no implicit way to pass environment changes from
	   a subshell back to its parent.

     { list; }
	   Compound construct; list is executed, but not in a subshell.  Note that '{' and '}'
	   are reserved words, not meta-characters.

     case word in [[(] pattern [| pat] ...) list [;; | ;& | ;| ]] ... esac
	   The case statement attempts to match word against a specified pattern; the list asso-
	   ciated with the first successfully matched pattern is executed.  Patterns used in case
	   statements are the same as those used for file name patterns except that the restric-
	   tions regarding '.' and '/' are dropped.  Note that any unquoted space before and
	   after a pattern is stripped; any space within a pattern must be quoted.  Both the word
	   and the patterns are subject to parameter, command, and arithmetic substitution, as
	   well as tilde substitution.

	   For historical reasons, open and close braces may be used instead of in and esac e.g.
	   case $foo { *) echo bar;; }.

	   The list terminators are:

	   ';;'  Terminate after the list.

	   ';&'  Fall through into the next list.

	   ';|'  Evaluate the remaining pattern-list tuples.

	   The exit status of a case statement is that of the executed list; if no list is exe-
	   cuted, the exit status is zero.

     for name [in word ...]; do list; done
	   For each word in the specified word list, the parameter name is set to the word and
	   list is executed.  If in is not used to specify a word list, the positional parameters
	   ($1, $2, etc.) are used instead.  For historical reasons, open and close braces may be
	   used instead of do and done e.g. for i; { echo $i; }.  The exit status of a for state-
	   ment is the last exit status of list; if list is never executed, the exit status is

     if list; then list; [elif list; then list;] ... [else list;] fi
	   If the exit status of the first list is zero, the second list is executed; otherwise,
	   the list following the elif, if any, is executed with similar consequences.	If all
	   the lists following the if and elifs fail (i.e. exit with non-zero status), the list
	   following the else is executed.  The exit status of an if statement is that of non-
	   conditional list that is executed; if no non-conditional list is executed, the exit
	   status is zero.

     select name [in word ...]; do list; done
	   The select statement provides an automatic method of presenting the user with a menu
	   and selecting from it.  An enumerated list of the specified word(s) is printed on
	   standard error, followed by a prompt (PS3: normally '#? ').	A number corresponding to
	   one of the enumerated words is then read from standard input, name is set to the
	   selected word (or unset if the selection is not valid), REPLY is set to what was read
	   (leading/trailing space is stripped), and list is executed.	If a blank line (i.e.
	   zero or more IFS octets) is entered, the menu is reprinted without executing list.

	   When list completes, the enumerated list is printed if REPLY is NULL, the prompt is
	   printed, and so on.	This process continues until an end-of-file is read, an interrupt
	   is received, or a break statement is executed inside the loop.  If ``in word ...'' is
	   omitted, the positional parameters are used (i.e. $1, $2, etc.).  For historical rea-
	   sons, open and close braces may be used instead of do and done e.g. select i; { echo
	   $i; }.  The exit status of a select statement is zero if a break statement is used to
	   exit the loop, non-zero otherwise.

     until list; do list; done
	   This works like while, except that the body is executed only while the exit status of
	   the first list is non-zero.

     while list; do list; done
	   A while is a pre-checked loop.  Its body is executed as often as the exit status of
	   the first list is zero.  The exit status of a while statement is the last exit status
	   of the list in the body of the loop; if the body is not executed, the exit status is

     function name { list; }
	   Defines the function name (see Functions below).  Note that redirections specified
	   after a function definition are performed whenever the function is executed, not when
	   the function definition is executed.

     name() command
	   Mostly the same as function (see Functions below).  Whitespace (space or tab) after
	   name will be ignored most of the time.

     function name() { list; }
	   The same as name() (bashism).  The function keyword is ignored.

     time [-p] [pipeline]
	   The Command execution section describes the time reserved word.

     (( expression ))
	   The arithmetic expression expression is evaluated; equivalent to ``let expression''
	   (see Arithmetic expressions and the let command, below).

     [[ expression ]]
	   Similar to the test and [ ... ] commands (described later), with the following excep-

	   o   Field splitting and file name generation are not performed on arguments.

	   o   The -a (AND) and -o (OR) operators are replaced with '&&' and '||', respectively.

	   o   Operators (e.g. '-f', '=', '!') must be unquoted.

	   o   Parameter, command, and arithmetic substitutions are performed as expressions are
	       evaluated and lazy expression evaluation is used for the '&&' and '||' operators.
	       This means that in the following statement, $(<foo) is evaluated if and only if
	       the file foo exists and is readable:

		     $ [[ -r foo && $(<foo) = b*r ]]

	   o   The second operand of the '!=' and '=' expressions are patterns (e.g. the compari-
	       son [[ foobar = f*r ]] succeeds).  This even works indirectly:

		     $ bar=foobar; baz='f*r'
		     $ [[ $bar = $baz ]]; echo $?
		     $ [[ $bar = "$baz" ]]; echo $?

	       Perhaps surprisingly, the first comparison succeeds, whereas the second doesn't.

     Quoting is used to prevent the shell from treating characters or words specially.	There are
     three methods of quoting.	First, '\' quotes the following character, unless it is at the
     end of a line, in which case both the '\' and the newline are stripped.  Second, a single
     quote (''') quotes everything up to the next single quote (this may span lines).  Third, a
     double quote ('"') quotes all characters, except '$', '`' and '\', up to the next unquoted
     double quote.  '$' and '`' inside double quotes have their usual meaning (i.e. parameter,
     command, or arithmetic substitution) except no field splitting is carried out on the results
     of double-quoted substitutions.  If a '\' inside a double-quoted string is followed by '\',
     '$', '`', or '"', it is replaced by the second character; if it is followed by a newline,
     both the '\' and the newline are stripped; otherwise, both the '\' and the character follow-
     ing are unchanged.

     If a single-quoted string is preceded by an unquoted '$', C style backslash expansion (see
     below) is applied (even single quote characters inside can be escaped and do not terminate
     the string then); the expanded result is treated as any other single-quoted string.  If a
     double-quoted string is preceded by an unquoted '$', the latter is ignored.

   Backslash expansion
     In places where backslashes are expanded, certain C and AT&T UNIX ksh or GNU bash style
     escapes are translated.  These include '\a', '\b', '\f', '\n', '\r', '\t', '\U########',
     '\u####', and '\v'.  For '\U########' and '\u####', ``#'' means a hexadecimal digit, of
     thich there may be none up to four or eight; these escapes translate a Unicode codepoint to
     UTF-8.  Furthermore, '\E' and '\e' expand to the escape character.

     In the print builtin mode, '\"', '\'', and '\?' are explicitly excluded; octal sequences
     must have the none up to three octal digits ``#'' prefixed with the digit zero ('\0###');
     hexadecimal sequences '\x##' are limited to none up to two hexadecimal digits ``#''; both
     octal and hexadecimal sequences convert to raw octets; '\#', where # is none of the above,
     translates to \# (backslashes are retained).

     Backslash expansion in the C style mode slightly differs: octal sequences '\###' must have
     no digit zero prefixing the one up to three octal digits ``#'' and yield raw octets; hexa-
     decimal sequences '\x#*' greedily eat up as many hexadecimal digits ``#'' as they can and
     terminate with the first non-hexadecimal digit; these translate a Unicode codepoint to
     UTF-8.  The sequence '\c#', where ``#'' is any octet, translates to Ctrl-# (which basically
     means, '\c?' becomes DEL, everything else is bitwise ANDed with 0x1F).  Finally, '\#', where
     # is none of the above, translates to # (has the backslash trimmed), even if it is a new-

     There are two types of aliases: normal command aliases and tracked aliases.  Command aliases
     are normally used as a short hand for a long or often used command.  The shell expands com-
     mand aliases (i.e. substitutes the alias name for its value) when it reads the first word of
     a command.  An expanded alias is re-processed to check for more aliases.  If a command alias
     ends in a space or tab, the following word is also checked for alias expansion.  The alias
     expansion process stops when a word that is not an alias is found, when a quoted word is
     found, or when an alias word that is currently being expanded is found.  Aliases are specif-
     ically an interactive feature: while they do happen to work in scripts and on the command
     line in some cases, aliases are expanded during lexing, so their use must be in a separate
     command tree from their definition; otherwise, the alias will not be found.  Noticeably,
     command lists (separated by semicolon, in command substitutions also by newline) may be one
     same parse tree.

     The following command aliases are defined automatically by the shell:

	   autoload='typeset -fu'
	   functions='typeset -f'
	   hash='alias -t'
	   history='fc -l'
	   integer='typeset -i'
	   login='exec login'
	   nameref='typeset -n'
	   nohup='nohup '
	   r='fc -e -'
	   stop='kill -STOP'
	   suspend='kill -STOP $$'
	   type='whence -v'

     Tracked aliases allow the shell to remember where it found a particular command.  The first
     time the shell does a path search for a command that is marked as a tracked alias, it saves
     the full path of the command.  The next time the command is executed, the shell checks the
     saved path to see that it is still valid, and if so, avoids repeating the path search.
     Tracked aliases can be listed and created using alias -t.	Note that changing the PATH
     parameter clears the saved paths for all tracked aliases.	If the trackall option is set
     (i.e. set -o trackall or set -h), the shell tracks all commands.  This option is set auto-
     matically for non-interactive shells.  For interactive shells, only the following commands
     are automatically tracked: cat(1), cc(1), chmod(1), cp(1), date(1), ed(1), emacs(1),
     grep(1), ls(1), make(1), mv(1), pr(1), rm(1), sed(1), sh(1), vi(1), and who(1).

     The first step the shell takes in executing a simple-command is to perform substitutions on
     the words of the command.	There are three kinds of substitution: parameter, command, and
     arithmetic.  Parameter substitutions, which are described in detail in the next section,
     take the form $name or ${...}; command substitutions take the form $(command) or (depre-
     cated) `command` or (executed in the current environment) ${ command;} and strip trailing
     newlines; and arithmetic substitutions take the form $((expression)).  Parsing the current-
     environment command substitution requires a space, tab or newline after the opening brace
     and that the closing brace be recognised as a keyword (i.e. is preceded by a newline or
     semicolon).  They are also called funsubs (function substitutions) and behave like functions
     in that local and return work, and in that exit terminates the parent shell.

     Another variant of substitution are the valsubs (value substitutions) ${|command;} which are
     also executed in the current environment, like funsubs, but share their I/O with the parent;
     instead, they evaluate to whatever the, initially empty, expression-local variable REPLY is
     set to within the commands.

     If a substitution appears outside of double quotes, the results of the substitution are gen-
     erally subject to word or field splitting according to the current value of the IFS parame-
     ter.  The IFS parameter specifies a list of octets which are used to break a string up into
     several words; any octets from the set space, tab, and newline that appear in the IFS octets
     are called ``IFS whitespace''.  Sequences of one or more IFS whitespace octets, in combina-
     tion with zero or one non-IFS whitespace octets, delimit a field.	As a special case, lead-
     ing and trailing IFS whitespace and trailing IFS non-whitespace are stripped (i.e. no lead-
     ing or trailing empty field is created by it); leading non-IFS whitespace does create an
     empty field.

     Example: If IFS is set to ``<space>:'', and VAR is set to
     ``<space>A<space>:<space><space>B::D'', the substitution for $VAR results in four fields:
     'A', 'B', '' (an empty field), and 'D'.  Note that if the IFS parameter is set to the NULL
     string, no field splitting is done; if the parameter is unset, the default value of space,
     tab, and newline is used.

     Also, note that the field splitting applies only to the immediate result of the substitu-
     tion.  Using the previous example, the substitution for $VAR:E results in the fields: 'A',
     'B', '', and 'D:E', not 'A', 'B', '', 'D', and 'E'.  This behavior is POSIX compliant, but
     incompatible with some other shell implementations which do field splitting on the word
     which contained the substitution or use IFS as a general whitespace delimiter.

     The results of substitution are, unless otherwise specified, also subject to brace expansion
     and file name expansion (see the relevant sections below).

     A command substitution is replaced by the output generated by the specified command which is
     run in a subshell.  For $(command) and ${ command;} substitutions, normal quoting rules are
     used when command is parsed; however, for the deprecated `command` form, a '\' followed by
     any of '$', '`', or '\' is stripped (a '\' followed by any other character is unchanged).
     As a special case in command substitutions, a command of the form <file is interpreted to
     mean substitute the contents of file.  Note that $(<foo) has the same effect as $(cat foo).

     Note that some shells do not use a recursive parser for command substitutions, leading to
     failure for certain constructs; to be portable, use as workaround 'x=$(cat) <<"EOF"' (or the
     newline-keeping 'x=<<"EOF"' extension) instead to merely slurp the string.  IEEE Std 1003.1
     (``POSIX.1'') recommends to use case statements of the form 'x=$(case $foo in (bar) echo
     $bar ;; (*) echo $baz ;; esac)' instead, which would work but not serve as example for this
     portability issue.

	   x=$(case $foo in bar) echo $bar ;; *) echo $baz ;; esac)
	   # above fails to parse on old shells; below is the workaround
	   x=$(eval $(cat)) <<"EOF"
	   case $foo in bar) echo $bar ;; *) echo $baz ;; esac

     Arithmetic substitutions are replaced by the value of the specified expression.  For exam-
     ple, the command print $((2+3*4)) displays 14.  See Arithmetic expressions for a description
     of an expression.

     Parameters are shell variables; they can be assigned values and their values can be accessed
     using a parameter substitution.  A parameter name is either one of the special single punc-
     tuation or digit character parameters described below, or a letter followed by zero or more
     letters or digits ('_' counts as a letter).  The latter form can be treated as arrays by
     appending an array index of the form [expr] where expr is an arithmetic expression.  Array
     indices in mksh are limited to the range 0 through 4294967295, inclusive.	That is, they are
     a 32-bit unsigned integer.

     Parameter substitutions take the form $name, ${name}, or ${name[expr]} where name is a
     parameter name.  Substitution of all array elements with ${name[*]} and ${name[@]} works
     equivalent to $* and $@ for positional parameters.  If substitution is performed on a param-
     eter (or an array parameter element) that is not set, a null string is substituted unless
     the nounset option (set -o nounset or set -u) is set, in which case an error occurs.

     Parameters can be assigned values in a number of ways.  First, the shell implicitly sets
     some parameters like '#', 'PWD', and '$'; this is the only way the special single character
     parameters are set.  Second, parameters are imported from the shell's environment at
     startup.  Third, parameters can be assigned values on the command line: for example, FOO=bar
     sets the parameter ``FOO'' to ``bar''; multiple parameter assignments can be given on a sin-
     gle command line and they can be followed by a simple-command, in which case the assignments
     are in effect only for the duration of the command (such assignments are also exported; see
     below for the implications of this).  Note that both the parameter name and the '=' must be
     unquoted for the shell to recognise a parameter assignment.  The construct FOO+=baz is also
     recognised; the old and new values are immediately concatenated.  The fourth way of setting
     a parameter is with the export, global, readonly, and typeset commands; see their descrip-
     tions in the Command execution section.  Fifth, for and select loops set parameters as well
     as the getopts, read, and set -A commands.  Lastly, parameters can be assigned values using
     assignment operators inside arithmetic expressions (see Arithmetic expressions below) or
     using the ${name=value} form of the parameter substitution (see below).

     Parameters with the export attribute (set using the export or typeset -x commands, or by
     parameter assignments followed by simple commands) are put in the environment (see
     environ(7)) of commands run by the shell as name=value pairs.  The order in which parameters
     appear in the environment of a command is unspecified.  When the shell starts up, it
     extracts parameters and their values from its environment and automatically sets the export
     attribute for those parameters.

     Modifiers can be applied to the ${name} form of parameter substitution:

	     If name is set and not NULL, it is substituted; otherwise, word is substituted.

	     If name is set and not NULL, word is substituted; otherwise, nothing is substituted.

	     If name is set and not NULL, it is substituted; otherwise, it is assigned word and
	     the resulting value of name is substituted.

	     If name is set and not NULL, it is substituted; otherwise, word is printed on stan-
	     dard error (preceded by name:) and an error occurs (normally causing termination of
	     a shell script, function, or script sourced using the '.' built-in).  If word is
	     omitted, the string ``parameter null or not set'' is used instead.  Currently a bug,
	     if word is a variable which expands to the null string, the error message is also

     Note that, for all of the above, word is actually considered quoted, and special parsing
     rules apply.  The parsing rules also differ on whether the expression is double-quoted: word
     then uses double-quoting rules, except for the double quote itself ('"') and the closing
     brace, which, if backslash escaped, gets quote removal applied.

     In the above modifiers, the ':' can be omitted, in which case the conditions only depend on
     name being set (as opposed to set and not NULL).  If word is needed, parameter, command,
     arithmetic, and tilde substitution are performed on it; if word is not needed, it is not

     The following forms of parameter substitution can also be used (if name is an array, its
     element #0 will be substituted in a scalar context):

	     The number of positional parameters if name is '*', '@', or not specified; otherwise
	     the length (in characters) of the string value of parameter name.

	     The number of elements in the array name.

	     The width (in screen columns) of the string value of parameter name, or -1 if
	     ${name} contains a control character.

	     The name of the variable referred to by name.  This will be name except when name is
	     a name reference (bound variable), created by the nameref command (which is an alias
	     for typeset -n).

	     The names of indices (keys) in the array name.

	     If pattern matches the beginning of the value of parameter name, the matched text is
	     deleted from the result of substitution.  A single '#' results in the shortest
	     match, and two of them result in the longest match.  Cannot be applied to a vector
	     (${*} or ${@} or ${array[*]} or ${array[@]}).

	     Like ${..#..} substitution, but it deletes from the end of the value.  Cannot be
	     applied to a vector.

	     Like ${..#..} substitution, but it replaces the longest match of pattern, anchored
	     anywhere in the value, with string.  If pattern begins with '#', it is anchored at
	     the beginning of the value; if it begins with '%', it is anchored at the end.  Pat-
	     terns that are empty or consist only of wildcards are invalid.  A single '/'
	     replaces the first occurence of the search pattern, and two of them replace all
	     occurences.  If /string is omitted, the pattern is replaced by the empty string,
	     i.e. deleted.  Cannot be applied to a vector.  Inefficiently implemented, may be

	     The first len characters of name, starting at position pos, are substituted.  Both
	     pos and :len are optional.  If pos is negative, counting starts at the end of the
	     string; if it is omitted, it defaults to 0.  If len is omitted or greater than the
	     length of the remaining string, all of it is substituted.	Both pos and len are
	     evaluated as arithmetic expressions.  Currently, pos must start with a space, open-
	     ing parenthesis or digit to be recognised.  Cannot be applied to a vector.

     ${name @#[seed]}
	     The internal hash of the expansion of name, with an optional (defaulting to zero)
	     [seed].  At the moment, this is NZAAT (a 32-bit hash based on Bob Jenkins' one-at-a-
	     time hash), but this is not set.  This is the hash the shell uses internally for its
	     associative arrays.

	     A quoted expression safe for re-entry, whose value is the value of the name parame-
	     ter, is substituted.

     Note that pattern may need extended globbing pattern (@(...)), single ('...') or double
     ("...") quote escaping unless -o sh is set.

     The following special parameters are implicitly set by the shell and cannot be set directly
     using assignments:

     !	     Process ID of the last background process started.  If no background processes have
	     been started, the parameter is not set.

     #	     The number of positional parameters ($1, $2, etc.).

     $	     The PID of the shell, or the PID of the original shell if it is a subshell.  Do NOT
	     use this mechanism for generating temporary file names; see mktemp(1) instead.

     -	     The concatenation of the current single letter options (see the set command below
	     for a list of options).

     ?	     The exit status of the last non-asynchronous command executed.  If the last command
	     was killed by a signal, $? is set to 128 plus the signal number.

     0	     The name of the shell, determined as follows: the first argument to mksh if it was
	     invoked with the -c option and arguments were given; otherwise the file argument, if
	     it was supplied; or else the basename the shell was invoked with (i.e. argv[0]).  $0
	     is also set to the name of the current script or the name of the current function,
	     if it was defined with the function keyword (i.e. a Korn shell style function).

     1 .. 9  The first nine positional parameters that were supplied to the shell, function, or
	     script sourced using the '.' built-in.  Further positional parameters may be
	     accessed using ${number}.

     *	     All positional parameters (except 0), i.e. $1, $2, $3, ...
	     If used outside of double quotes, parameters are separate words (which are subjected
	     to word splitting); if used within double quotes, parameters are separated by the
	     first character of the IFS parameter (or the empty string if IFS is NULL).

     @	     Same as $*, unless it is used inside double quotes, in which case a separate word is
	     generated for each positional parameter.  If there are no positional parameters, no
	     word is generated.  $@ can be used to access arguments, verbatim, without losing
	     NULL arguments or splitting arguments with spaces.

     The following parameters are set and/or used by the shell:

     _		  (underscore) When an external command is executed by the shell, this parameter
		  is set in the environment of the new process to the path of the executed com-
		  mand.  In interactive use, this parameter is also set in the parent shell to
		  the last word of the previous command.

     BASHPID	  The PID of the shell or subshell.

     CDPATH	  Search path for the cd built-in command.  It works the same way as PATH for
		  those directories not beginning with '/' in cd commands.  Note that if CDPATH
		  is set and does not contain '.' or contains an empty path, the current direc-
		  tory is not searched.  Also, the cd built-in command will display the resulting
		  directory when a match is found in any search path other than the empty path.

     COLUMNS	  Set to the number of columns on the terminal or window.  Always set, defaults
		  to 80, unless the value as reported by stty(1) is non-zero and sane enough
		  (minimum is 12x3); similar for LINES.  This parameter is used by the interac-
		  tive line editing modes, and by the select, set -o, and kill -l commands to
		  format information columns.  Importing from the environment or unsetting this
		  parameter removes the binding to the actual terminal size in favour of the pro-
		  vided value.

     ENV	  If this parameter is found to be set after any profile files are executed, the
		  expanded value is used as a shell startup file.  It typically contains function
		  and alias definitions.

     ERRNO	  Integer value of the shell's errno variable.	It indicates the reason the last
		  system call failed.  Not yet implemented.

     EXECSHELL	  If set, this parameter is assumed to contain the shell that is to be used to
		  execute commands that execve(2) fails to execute and which do not start with a
		  ``#!shell'' sequence.

     FCEDIT	  The editor used by the fc command (see below).

     FPATH	  Like PATH, but used when an undefined function is executed to locate the file
		  defining the function.  It is also searched when a command can't be found using
		  PATH.  See Functions below for more information.

     HISTFILE	  The name of the file used to store command history.  When assigned to, history
		  is loaded from the specified file.  Also, several invocations of the shell will
		  share history if their HISTFILE parameters all point to the same file.

		  Note: If HISTFILE isn't set, no history file is used.  This is different from
		  AT&T UNIX ksh.

     HISTSIZE	  The number of commands normally stored for history.  The default is 2047.

     HOME	  The default directory for the cd command and the value substituted for an
		  unqualified ~ (see Tilde expansion below).

     IFS	  Internal field separator, used during substitution and by the read command, to
		  split values into distinct arguments; normally set to space, tab, and newline.
		  See Substitution above for details.

		  Note: This parameter is not imported from the environment when the shell is

     KSHEGID	  The effective group id of the shell.

     KSHGID	  The real group id of the shell.

     KSHUID	  The real user id of the shell.

     KSH_VERSION  The name and version of the shell (read-only).  See also the version commands
		  in Emacs editing mode and Vi editing mode sections, below.

     LINENO	  The line number of the function or shell script that is currently being exe-

     LINES	  Set to the number of lines on the terminal or window.  Always set, defaults to
		  24.  See COLUMNS.

		  Time since the epoch, as returned by gettimeofday(2), formatted as decimal
		  tv_sec followed by a dot ('.') and tv_usec padded to exactly six decimal dig-

     OLDPWD	  The previous working directory.  Unset if cd has not successfully changed
		  directories since the shell started, or if the shell doesn't know where it is.

     OPTARG	  When using getopts, it contains the argument for a parsed option, if it
		  requires one.

     OPTIND	  The index of the next argument to be processed when using getopts.  Assigning 1
		  to this parameter causes getopts to process arguments from the beginning the
		  next time it is invoked.

     PATH	  A colon separated list of directories that are searched when looking for com-
		  mands and files sourced using the '.' command (see below).  An empty string
		  resulting from a leading or trailing colon, or two adjacent colons, is treated
		  as a '.' (the current directory).

     PGRP	  The process ID of the shell's process group leader.

     PIPESTATUS   An array containing the errorlevel (exit status) codes, one by one, of the last
		  pipeline run in the foreground.

     PPID	  The process ID of the shell's parent.

     PS1	  The primary prompt for interactive shells.  Parameter, command, and arithmetic
		  substitutions are performed, and '!' is replaced with the current command num-
		  ber (see the fc command below).  A literal '!' can be put in the prompt by
		  placing '!!' in PS1.

		  The default prompt is '$ ' for non-root users, '# ' for root.  If mksh is
		  invoked by root and PS1 does not contain a '#' character, the default value
		  will be used even if PS1 already exists in the environment.

		  The mksh distribution comes with a sample dot.mkshrc containing a sophisticated
		  example, but you might like the following one (note that ${HOSTNAME:=$(host-
		  name)} and the root-vs-user distinguishing clause are (in this example) exe-
		  cuted at PS1 assignment time, while the $USER and $PWD are escaped and thus
		  will be evaluated each time a prompt is displayed):

		  PS1='${USER:=$(id -un)}'"@${HOSTNAME:=$(hostname)}:\$PWD $(
			  if (( USER_ID )); then print \$; else print \#; fi) "

		  Note that since the command-line editors try to figure out how long the prompt
		  is (so they know how far it is to the edge of the screen), escape codes in the
		  prompt tend to mess things up.  You can tell the shell not to count certain
		  sequences (such as escape codes) by prefixing your prompt with a character
		  (such as Ctrl-A) followed by a carriage return and then delimiting the escape
		  codes with this character.  Any occurences of that character in the prompt are
		  not printed.	By the way, don't blame me for this hack; it's derived from the
		  original ksh88(1), which did print the delimiter character so you were out of
		  luck if you did not have any non-printing characters.

		  Since Backslashes and other special characters may be interpreted by the shell,
		  to set PS1 either escape the backslash itself, or use double quotes.	The lat-
		  ter is more practical.  This is a more complex example, avoiding to directly
		  enter special characters (for example with ^V in the emacs editing mode), which
		  embeds the current working directory, in reverse video (colour would work,
		  too), in the prompt string:

			x=$(print \\001)
			PS1="$x$(print \\r)$x$(tput smso)$x\$PWD$x$(tput rmso)$x> "

		  Due to a strong suggestion from David G. Korn, mksh now also supports the fol-
		  lowing form:

			PS1=$'\1\r\1\e[7m\1$PWD\1\e[0m\1> '

     PS2	  Secondary prompt string, by default '> ', used when more input is needed to
		  complete a command.

     PS3	  Prompt used by the select statement when reading a menu selection.  The default
		  is '#? '.

     PS4	  Used to prefix commands that are printed during execution tracing (see the set
		  -x command below).  Parameter, command, and arithmetic substitutions are per-
		  formed before it is printed.	The default is '+ '.  You may want to set it to
		  '[$EPOCHREALTIME] ' instead, to include timestamps.

     PWD	  The current working directory.  May be unset or NULL if the shell doesn't know
		  where it is.

     RANDOM	  Each time RANDOM is referenced, it is assigned a number between 0 and 32767
		  from a Linear Congruential PRNG first.

     REPLY	  Default parameter for the read command if no names are given.  Also used in
		  select loops to store the value that is read from standard input.

     SECONDS	  The number of seconds since the shell started or, if the parameter has been
		  assigned an integer value, the number of seconds since the assignment plus the
		  value that was assigned.

     TMOUT	  If set to a positive integer in an interactive shell, it specifies the maximum
		  number of seconds the shell will wait for input after printing the primary
		  prompt (PS1).  If the time is exceeded, the shell exits.

     TMPDIR	  The directory temporary shell files are created in.  If this parameter is not
		  set, or does not contain the absolute path of a writable directory, temporary
		  files are created in /tmp.

     USER_ID	  The effective user id of the shell.

   Tilde expansion
     Tilde expansion which is done in parallel with parameter substitution, is done on words
     starting with an unquoted '~'.  The characters following the tilde, up to the first '/', if
     any, are assumed to be a login name.  If the login name is empty, '+', or '-', the value of
     the HOME, PWD, or OLDPWD parameter is substituted, respectively.  Otherwise, the password
     file is searched for the login name, and the tilde expression is substituted with the user's
     home directory.  If the login name is not found in the password file or if any quoting or
     parameter substitution occurs in the login name, no substitution is performed.

     In parameter assignments (such as those preceding a simple-command or those occurring in the
     arguments of alias, export, global, readonly, and typeset), tilde expansion is done after
     any assignment (i.e. after the equals sign) or after an unquoted colon (':'); login names
     are also delimited by colons.

     The home directory of previously expanded login names are cached and re-used.  The alias -d
     command may be used to list, change, and add to this cache (e.g. alias -d
     fac=/usr/local/facilities; cd ~fac/bin).

   Brace expansion (alteration)
     Brace expressions take the following form:


     The expressions are expanded to N words, each of which is the concatenation of prefix, stri,
     and suffix (e.g. ``a{c,b{X,Y},d}e'' expands to four words: ``ace'', ``abXe'', ``abYe'', and
     ``ade'').	As noted in the example, brace expressions can be nested and the resulting words
     are not sorted.  Brace expressions must contain an unquoted comma (',') for expansion to
     occur (e.g. {} and {foo} are not expanded).  Brace expansion is carried out after parameter
     substitution and before file name generation.

   File name patterns
     A file name pattern is a word containing one or more unquoted '?', '*', '+', '@', or '!'
     characters or ``[..]'' sequences.	Once brace expansion has been performed, the shell
     replaces file name patterns with the sorted names of all the files that match the pattern
     (if no files match, the word is left unchanged).  The pattern elements have the following

     ?	     Matches any single character.

     *	     Matches any sequence of octets.

     [..]    Matches any of the octets inside the brackets.  Ranges of octets can be specified by
	     separating two octets by a '-' (e.g. ``[a0-9]'' matches the letter 'a' or any
	     digit).  In order to represent itself, a '-' must either be quoted or the first or
	     last octet in the octet list.  Similarly, a ']' must be quoted or the first octet in
	     the list if it is to represent itself instead of the end of the list.  Also, a '!'
	     appearing at the start of the list has special meaning (see below), so to represent
	     itself it must be quoted or appear later in the list.

     [!..]   Like [..], except it matches any octet not inside the brackets.

	     Matches any string of octets that matches zero or more occurrences of the specified
	     patterns.	Example: The pattern *(foo|bar) matches the strings ``'', ``foo'',
	     ``bar'', ``foobarfoo'', etc.

	     Matches any string of octets that matches one or more occurrences of the specified
	     patterns.	Example: The pattern +(foo|bar) matches the strings ``foo'', ``bar'',
	     ``foobar'', etc.

	     Matches the empty string or a string that matches one of the specified patterns.
	     Example: The pattern ?(foo|bar) only matches the strings ``'', ``foo'', and ``bar''.

	     Matches a string that matches one of the specified patterns.  Example: The pattern
	     @(foo|bar) only matches the strings ``foo'' and ``bar''.

	     Matches any string that does not match one of the specified patterns.  Examples: The
	     pattern !(foo|bar) matches all strings except ``foo'' and ``bar''; the pattern !(*)
	     matches no strings; the pattern !(?)* matches all strings (think about it).

     Note that complicated globbing, especially with alternatives, is slow; using separate com-
     parisons may (or may not) be faster.

     Note that mksh (and pdksh) never matches '.' and '..', but AT&T UNIX ksh, Bourne sh, and GNU
     bash do.

     Note that none of the above pattern elements match either a period ('.') at the start of a
     file name or a slash ('/'), even if they are explicitly used in a [..] sequence; also, the
     names '.' and '..' are never matched, even by the pattern '.*'.

     If the markdirs option is set, any directories that result from file name generation are
     marked with a trailing '/'.

   Input/output redirection
     When a command is executed, its standard input, standard output, and standard error (file
     descriptors 0, 1, and 2, respectively) are normally inherited from the shell.  Three excep-
     tions to this are commands in pipelines, for which standard input and/or standard output are
     those set up by the pipeline, asynchronous commands created when job control is disabled,
     for which standard input is initially set to be from /dev/null, and commands for which any
     of the following redirections have been specified:

     > file	 Standard output is redirected to file.  If file does not exist, it is created;
		 if it does exist, is a regular file, and the noclobber option is set, an error
		 occurs; otherwise, the file is truncated.  Note that this means the command cmd
		 <foo >foo will open foo for reading and then truncate it when it opens it for
		 writing, before cmd gets a chance to actually read foo.

     >| file	 Same as >, except the file is truncated, even if the noclobber option is set.

     >> file	 Same as >, except if file exists it is appended to instead of being truncated.
		 Also, the file is opened in append mode, so writes always go to the end of the
		 file (see open(2)).

     < file	 Standard input is redirected from file, which is opened for reading.

     <> file	 Same as <, except the file is opened for reading and writing.

     << marker	 After reading the command line containing this kind of redirection (called a
		 ``here document''), the shell copies lines from the command source into a tempo-
		 rary file until a line matching marker is read.  When the command is executed,
		 standard input is redirected from the temporary file.	If marker contains no
		 quoted characters, the contents of the temporary file are processed as if
		 enclosed in double quotes each time the command is executed, so parameter, com-
		 mand, and arithmetic substitutions are performed, along with backslash ('\')
		 escapes for '$', '`', '\', and '\newline', but not for '"'.  If multiple here
		 documents are used on the same command line, they are saved in order.

		 If no marker is given, the here document ends at the next << and substitution
		 will be performed.  If marker is only a set of either single ``'''' or double
		 '""' quotes with nothing in between, the here document ends at the next empty
		 line and substitution will not be performed.

     <<- marker  Same as <<, except leading tabs are stripped from lines in the here document.

     <<< word	 Same as <<, except that word is the here document.  This is called a here

     <& fd	 Standard input is duplicated from file descriptor fd.	fd can be a number, indi-
		 cating the number of an existing file descriptor; the letter 'p', indicating the
		 file descriptor associated with the output of the current co-process; or the
		 character '-', indicating standard input is to be closed.  Note that fd is lim-
		 ited to a single digit in most shell implementations.

     >& fd	 Same as <&, except the operation is done on standard output.

     &> file	 Same as > file 2>&1.  This is a GNU bash extension supported by mksh which also
		 supports the preceding explicit fd number, for example, 3&> file is the same as
		 3> file 2>&3 in mksh but a syntax error in GNU bash.  Setting the -o posix or -o
		 sh shell options disable parsing of this redirection; it's a compatibility fea-
		 ture to legacy scripts, to not be used when writing new shell code.

     &>| file, &>> file, &>& fd
		 Same as >| file, >> file, or >& fd, followed by 2>&1, as above.  These are mksh

     In any of the above redirections, the file descriptor that is redirected (i.e. standard
     input or standard output) can be explicitly given by preceding the redirection with a number
     (portably, only a single digit).  Parameter, command, and arithmetic substitutions, tilde
     substitutions, and (if the shell is interactive) file name generation are all performed on
     the file, marker, and fd arguments of redirections.  Note, however, that the results of any
     file name generation are only used if a single file is matched; if multiple files match, the
     word with the expanded file name generation characters is used.  Note that in restricted
     shells, redirections which can create files cannot be used.

     For simple-commands, redirections may appear anywhere in the command; for compound-commands
     (if statements, etc.), any redirections must appear at the end.  Redirections are processed
     after pipelines are created and in the order they are given, so the following will print an
     error with a line number prepended to it:

	   $ cat /foo/bar 2>&1 >/dev/null | pr -n -t

     File descriptors created by input/output redirections are private to the Korn shell, but
     passed to sub-processes if -o posix or -o sh is set.

   Arithmetic expressions
     Integer arithmetic expressions can be used with the let command, inside $((..)) expressions,
     inside array references (e.g. name[expr]), as numeric arguments to the test command, and as
     the value of an assignment to an integer parameter.

     Expressions are calculated using signed arithmetic and the mksh_ari_t type (a 32-bit signed
     integer), unless they begin with a sole '#' character, in which case they use mksh_uari_t (a
     32-bit unsigned integer).

     Expressions may contain alpha-numeric parameter identifiers, array references, and integer
     constants and may be combined with the following C operators (listed and grouped in increas-
     ing order of precedence):

     Unary operators:

	   + - ! ~ ++ --

     Binary operators:

	   = += -= *= /= %= <<<= >>>= <<= >>= &= ^= |=
	   == !=
	   < <= > >=
	   <<< >>> << >>
	   + -
	   * / %

     Ternary operators:

	   ?: (precedence is immediately higher than assignment)

     Grouping operators:

	   ( )

     Integer constants and expressions are calculated using an exactly 32-bit wide, signed or
     unsigned, type with silent wraparound on integer overflow.  Integer constants may be speci-
     fied with arbitrary bases using the notation base#number, where base is a decimal integer
     specifying the base, and number is a number in the specified base.  Additionally, base-16
     integers may be specified by prefixing them with '0x' (case-insensitive) in all forms of
     arithmetic expressions, except as numeric arguments to the test built-in command.	Prefixing
     numbers with a sole digit zero ('0') leads to the shell interpreting it as base-8 integer in
     posix mode only; historically, (pd)ksh has never done so either anyway, and it's unsafe to
     do that, but POSIX demands it nowadays.  As a special mksh extension, numbers to the base of
     one are treated as either (8-bit transparent) ASCII or Unicode codepoints, depending on the
     shell's utf8-mode flag (current setting).	The AT&T UNIX ksh93 syntax of ``'x''' instead of
     ``1#x'' is also supported.  Note that NUL bytes (integral value of zero) cannot be used.  An
     unset or empty parameter evaluates to 0 in integer context.  In Unicode mode, raw octets are
     mapped into the range EF80..EFFF as in OPTU-8, which is in the PUA and has been assigned by
     CSUR for this use.  If more than one octet in ASCII mode, or a sequence of more than one
     octet not forming a valid and minimal CESU-8 sequence is passed, the behaviour is undefined
     (usually, the shell aborts with a parse error, but rarely, it succeeds, e.g. on the sequence
     C2 20).  That's why you should always use ASCII mode unless you know that the input is well-
     formed UTF-8 in the range of 0000..FFFD.

     The operators are evaluated as follows:

	   unary +
		   Result is the argument (included for completeness).

	   unary -

	   !	   Logical NOT; the result is 1 if argument is zero, 0 if not.

	   ~	   Arithmetic (bit-wise) NOT.

	   ++	   Increment; must be applied to a parameter (not a literal or other expression).
		   The parameter is incremented by 1.  When used as a prefix operator, the result
		   is the incremented value of the parameter; when used as a postfix operator,
		   the result is the original value of the parameter.

	   --	   Similar to ++, except the parameter is decremented by 1.

	   ,	   Separates two arithmetic expressions; the left-hand side is evaluated first,
		   then the right.  The result is the value of the expression on the right-hand

	   =	   Assignment; the variable on the left is set to the value on the right.

	   += -= *= /= %= <<<= >>>= <<= >>= &= ^= |=
		   Assignment operators.  <var><op>=<expr> is the same as <var>=<var><op><expr>,
		   with any operator precedence in <expr> preserved.  For example, ``var1 *= 5 +
		   3'' is the same as specifying ``var1 = var1 * (5 + 3)''.

	   ||	   Logical OR; the result is 1 if either argument is non-zero, 0 if not.  The
		   right argument is evaluated only if the left argument is zero.

	   &&	   Logical AND; the result is 1 if both arguments are non-zero, 0 if not.  The
		   right argument is evaluated only if the left argument is non-zero.

	   |	   Arithmetic (bit-wise) OR.

	   ^	   Arithmetic (bit-wise) XOR (exclusive-OR).

	   &	   Arithmetic (bit-wise) AND.

	   ==	   Equal; the result is 1 if both arguments are equal, 0 if not.

	   !=	   Not equal; the result is 0 if both arguments are equal, 1 if not.

	   <	   Less than; the result is 1 if the left argument is less than the right, 0 if

	   <= > >=
		   Less than or equal, greater than or equal, greater than.  See <.

	   <<< >>>
		   Rotate left (right); the result is similar to shift (see <<) except that the
		   bits shifted out at one end are shifted in at the other end, instead of zero
		   or sign bits.

	   << >>   Shift left (right); the result is the left argument with its bits shifted left
		   (right) by the amount given in the right argument.

	   + - * /
		   Addition, subtraction, multiplication, and division.

	   %	   Remainder; the result is the remainder of the division of the left argument by
		   the right.

		   If <arg1> is non-zero, the result is <arg2>; otherwise the result is <arg3>.
		   The non-result argument is not evaluated.

     A co-process (which is a pipeline created with the '|&' operator) is an asynchronous process
     that the shell can both write to (using print -p) and read from (using read -p).  The input
     and output of the co-process can also be manipulated using >&p and <&p redirections, respec-
     tively.  Once a co-process has been started, another can't be started until the co-process
     exits, or until the co-process's input has been redirected using an exec n>&p redirection.
     If a co-process's input is redirected in this way, the next co-process to be started will
     share the output with the first co-process, unless the output of the initial co-process has
     been redirected using an exec n<&p redirection.

     Some notes concerning co-processes:

     o	 The only way to close the co-process's input (so the co-process reads an end-of-file) is
	 to redirect the input to a numbered file descriptor and then close that file descriptor:
	 exec 3>&p; exec 3>&-

     o	 In order for co-processes to share a common output, the shell must keep the write por-
	 tion of the output pipe open.	This means that end-of-file will not be detected until
	 all co-processes sharing the co-process's output have exited (when they all exit, the
	 shell closes its copy of the pipe).  This can be avoided by redirecting the output to a
	 numbered file descriptor (as this also causes the shell to close its copy).  Note that
	 this behaviour is slightly different from the original Korn shell which closes its copy
	 of the write portion of the co-process output when the most recently started co-process
	 (instead of when all sharing co-processes) exits.

     o	 print -p will ignore SIGPIPE signals during writes if the signal is not being trapped or
	 ignored; the same is true if the co-process input has been duplicated to another file
	 descriptor and print -un is used.

     Functions are defined using either Korn shell function function-name syntax or the
     Bourne/POSIX shell function-name() syntax (see below for the difference between the two
     forms).  Functions are like .-scripts (i.e. scripts sourced using the '.' built-in) in that
     they are executed in the current environment.  However, unlike .-scripts, shell arguments
     (i.e. positional parameters $1, $2, etc.) are never visible inside them.  When the shell is
     determining the location of a command, functions are searched after special built-in com-
     mands, before builtins and the PATH is searched.

     An existing function may be deleted using unset -f function-name.	A list of functions can
     be obtained using typeset +f and the function definitions can be listed using typeset -f.
     The autoload command (which is an alias for typeset -fu) may be used to create undefined
     functions: when an undefined function is executed, the shell searches the path specified in
     the FPATH parameter for a file with the same name as the function which, if found, is read
     and executed.  If after executing the file the named function is found to be defined, the
     function is executed; otherwise, the normal command search is continued (i.e. the shell
     searches the regular built-in command table and PATH).  Note that if a command is not found
     using PATH, an attempt is made to autoload a function using FPATH (this is an undocumented
     feature of the original Korn shell).

     Functions can have two attributes, ``trace'' and ``export'', which can be set with typeset
     -ft and typeset -fx, respectively.  When a traced function is executed, the shell's xtrace
     option is turned on for the function's duration.  The ``export'' attribute of functions is
     currently not used.  In the original Korn shell, exported functions are visible to shell
     scripts that are executed.

     Since functions are executed in the current shell environment, parameter assignments made
     inside functions are visible after the function completes.  If this is not the desired
     effect, the typeset command can be used inside a function to create a local parameter.  Note
     that AT&T UNIX ksh93 uses static scoping (one global scope, one local scope per function)
     and allows local variables only on Korn style functions, whereas mksh uses dynamic scoping
     (nested scopes of varying locality).  Note that special parameters (e.g. $$, $!) can't be
     scoped in this way.

     The exit status of a function is that of the last command executed in the function.  A func-
     tion can be made to finish immediately using the return command; this may also be used to
     explicitly specify the exit status.

     Functions defined with the function reserved word are treated differently in the following
     ways from functions defined with the () notation:

     o	 The $0 parameter is set to the name of the function (Bourne-style functions leave $0

     o	 Parameter assignments preceding function calls are not kept in the shell environment
	 (executing Bourne-style functions will keep assignments).

     o	 OPTIND is saved/reset and restored on entry and exit from the function so getopts can be
	 used properly both inside and outside the function (Bourne-style functions leave OPTIND
	 untouched, so using getopts inside a function interferes with using getopts outside the

     o	 Bourne-style function definitions take precedence over alias dereferences and remove
	 alias definitions upon encounter, while aliases take precedence over Korn-style func-

     In the future, the following differences may also be added:

     o	 A separate trap/signal environment will be used during the execution of functions.  This
	 will mean that traps set inside a function will not affect the shell's traps and signals
	 that are not ignored in the shell (but may be trapped) will have their default effect in
	 a function.

     o	 The EXIT trap, if set in a function, will be executed after the function returns.

   Command execution
     After evaluation of command-line arguments, redirections, and parameter assignments, the
     type of command is determined: a special built-in command, a function, a normal builtin, or
     the name of a file to execute found using the PATH parameter.  The checks are made in the
     above order.  Special built-in commands differ from other commands in that the PATH parame-
     ter is not used to find them, an error during their execution can cause a non-interactive
     shell to exit, and parameter assignments that are specified before the command are kept
     after the command completes.  Regular built-in commands are different only in that the PATH
     parameter is not used to find them.

     The original ksh and POSIX differ somewhat in which commands are considered special or regu-

     POSIX special built-in utilities:

     ., :, break, continue, eval, exec, exit, export, readonly, return, set, shift, times, trap,

     Additional mksh commands keeping assignments:

     builtin, global, typeset, wait

     Builtins that are not special:

     [, alias, bg, bind, cat, cd, command, echo, false, fc, fg, getopts, jobs, kill, let, mknod,
     print, pwd, read, realpath, rename, sleep, test, true, ulimit, umask, unalias, whence

     Once the type of command has been determined, any command-line parameter assignments are
     performed and exported for the duration of the command.

     The following describes the special and regular built-in commands:

     . file [arg ...]
	    This is called the ``dot'' command.  Execute the commands in file in the current
	    environment.  The file is searched for in the directories of PATH.	If arguments are
	    given, the positional parameters may be used to access them while file is being exe-
	    cuted.  If no arguments are given, the positional parameters are those of the envi-
	    ronment the command is used in.

     : [...]
	    The null command.  Exit status is set to zero.

     [ expression ]
	    See test.

     alias [-d | -t [-r] | +-x] [-p] [+] [name [=value] ...]
	    Without arguments, alias lists all aliases.  For any name without a value, the exist-
	    ing alias is listed.  Any name with a value defines an alias (see Aliases above).

	    When listing aliases, one of two formats is used.  Normally, aliases are listed as
	    name=value, where value is quoted.	If options were preceded with '+', or a lone '+'
	    is given on the command line, only name is printed.

	    The -d option causes directory aliases which are used in tilde expansion to be listed
	    or set (see Tilde expansion above).

	    If the -p option is used, each alias is prefixed with the string ``alias ''.

	    The -t option indicates that tracked aliases are to be listed/set (values specified
	    on the command line are ignored for tracked aliases).  The -r option indicates that
	    all tracked aliases are to be reset.

	    The -x option sets (+x clears) the export attribute of an alias, or, if no names are
	    given, lists the aliases with the export attribute (exporting an alias has no

     bg [job ...]
	    Resume the specified stopped job(s) in the background.  If no jobs are specified, %+
	    is assumed.  See Job control below for more information.

     bind [-l]
	    The current bindings are listed.  If the -l flag is given, bind instead lists the
	    names of the functions to which keys may be bound.	See Emacs editing mode for more

     bind [-m] string=[substitute] ...
     bind string=[editing-command] ...
	    The specified editing command is bound to the given string, which should consist of a
	    control character optionally preceded by one of the two prefix characters and option-
	    ally succeded by a tilde character.  Future input of the string will cause the edit-
	    ing command to be immediately invoked.  If the -m flag is given, the specified input
	    string will afterwards be immediately replaced by the given substitute string which
	    may contain editing commands but not other macros.	If a tilde postfix is given, a
	    tilde trailing the one or two prefices and the control character is ignored, any
	    other trailing character will be processed afterwards.

	    Control characters may be written using caret notation i.e. ^X represents Ctrl-X.
	    Note that although only two prefix characters (usually ESC and ^X) are supported,
	    some multi-character sequences can be supported.

	    The following default bindings show how the arrow keys, the home, end and delete key
	    on a BSD wsvt25, xterm-xfree86 or GNU screen terminal are bound (of course some
	    escape sequences won't work out quite this nicely):

		  bind '^X'=prefix-2
		  bind '^[['=prefix-2
		  bind '^XA'=up-history
		  bind '^XB'=down-history
		  bind '^XC'=forward-char
		  bind '^XD'=backward-char
		  bind '^X1~'=beginning-of-line
		  bind '^X7~'=beginning-of-line
		  bind '^XH'=beginning-of-line
		  bind '^X4~'=end-of-line
		  bind '^X8~'=end-of-line
		  bind '^XF'=end-of-line
		  bind '^X3~'=delete-char-forward

     break [level]
	    Exit the levelth inner-most for, select, until, or while loop.  level defaults to 1.

     builtin [--] command [arg ...]
	    Execute the built-in command command.

     cat [-u] [file ...]
	    Read files sequentially, in command line order, and write them to standard output.
	    If a file is a single dash ('-') or absent, read from standard input.  Unless com-
	    piled with MKSH_NO_EXTERNAL_CAT, if any options are given, an external cat(1) utility
	    is invoked instead if called from the shell.  For direct builtin calls, the POSIX -u
	    option is supported as a no-op.

     cd [-L] [dir]
     cd -P [-e] [dir]
     chdir [-eLP] [dir]
	    Set the working directory to dir.  If the parameter CDPATH is set, it lists the
	    search path for the directory containing dir.  A NULL path means the current direc-
	    tory.  If dir is found in any component of the CDPATH search path other than the NULL
	    path, the name of the new working directory will be written to standard output.  If
	    dir is missing, the home directory HOME is used.  If dir is '-', the previous working
	    directory is used (see the OLDPWD parameter).

	    If the -L option (logical path) is used or if the physical option isn't set (see the
	    set command below), references to '..' in dir are relative to the path used to get to
	    the directory.  If the -P option (physical path) is used or if the physical option is
	    set, '..' is relative to the filesystem directory tree.  The PWD and OLDPWD parame-
	    ters are updated to reflect the current and old working directory, respectively.  If
	    the -e option is set for physical filesystem traversal, and PWD could not be set, the
	    exit code is 1; greater than 1 if an error occurred, 0 otherwise.

     cd [-eLP] old new
     chdir [-eLP] old new
	    The string new is substituted for old in the current directory, and the shell
	    attempts to change to the new directory.

     command [-pVv] cmd [arg ...]
	    If neither the -v nor -V option is given, cmd is executed exactly as if command had
	    not been specified, with two exceptions: firstly, cmd cannot be a shell function; and
	    secondly, special built-in commands lose their specialness (i.e. redirection and
	    utility errors do not cause the shell to exit, and command assignments are not perma-

	    If the -p option is given, a default search path is used instead of the current value
	    of PATH, the actual value of which is system dependent.

	    If the -v option is given, instead of executing cmd, information about what would be
	    executed is given (and the same is done for arg ...).  For special and regular built-
	    in commands and functions, their names are simply printed; for aliases, a command
	    that defines them is printed; and for commands found by searching the PATH parameter,
	    the full path of the command is printed.  If no command is found (i.e. the path
	    search fails), nothing is printed and command exits with a non-zero status.  The -V
	    option is like the -v option, except it is more verbose.

     continue [level]
	    Jumps to the beginning of the levelth inner-most for, select, until, or while loop.
	    level defaults to 1.

     echo [-Een] [arg ...]
	    Warning: this utility is not portable; use the Korn shell builtin print instead.

	    Prints its arguments (separated by spaces) followed by a newline, to the standard
	    output.  The newline is suppressed if any of the arguments contain the backslash
	    sequence '\c'.  See the print command below for a list of other backslash sequences
	    that are recognised.

	    The options are provided for compatibility with BSD shell scripts.	The -n option
	    suppresses the trailing newline, -e enables backslash interpretation (a no-op, since
	    this is normally done), and -E suppresses backslash interpretation.

	    If the posix or sh option is set or this is a direct builtin call, only the first
	    argument is treated as an option, and only if it is exactly ``-n''.  Backslash inter-
	    pretation is disabled.

     eval command ...
	    The arguments are concatenated (with spaces between them) to form a single string
	    which the shell then parses and executes in the current environment.

     exec [command [arg ...]]
	    The command is executed without forking, replacing the shell process.

	    If no command is given except for I/O redirection, the I/O redirection is permanent
	    and the shell is not replaced.  Any file descriptors greater than 2 which are opened
	    or dup(2)'d in this way are not made available to other executed commands (i.e. com-
	    mands that are not built-in to the shell).	Note that the Bourne shell differs here;
	    it does pass these file descriptors on.

     exit [status]
	    The shell exits with the specified exit status.  If status is not specified, the exit
	    status is the current value of the $? parameter.

     export [-p] [parameter[=value]]
	    Sets the export attribute of the named parameters.	Exported parameters are passed in
	    the environment to executed commands.  If values are specified, the named parameters
	    are also assigned.

	    If no parameters are specified, all parameters with the export attribute set are
	    printed one per line; either their names, or, if a '-' with no option letter is spec-
	    ified, name=value pairs, or, with -p, export commands suitable for re-entry.

     false  A command that exits with a non-zero status.

     fc [-e editor | -l [-n]] [-r] [first [last]]
	    first and last select commands from the history.  Commands can be selected by history
	    number or a string specifying the most recent command starting with that string.  The
	    -l option lists the command on standard output, and -n inhibits the default command
	    numbers.  The -r option reverses the order of the list.  Without -l, the selected
	    commands are edited by the editor specified with the -e option, or if no -e is speci-
	    fied, the editor specified by the FCEDIT parameter (if this parameter is not set,
	    /bin/ed is used), and then executed by the shell.

     fc -e - | -s [-g] [old=new] [prefix]
	    Re-execute the selected command (the previous command by default) after performing
	    the optional substitution of old with new.	If -g is specified, all occurrences of
	    old are replaced with new.	The meaning of -e - and -s is identical: re-execute the
	    selected command without invoking an editor.  This command is usually accessed with
	    the predefined: alias r='fc -e -'

     fg [job ...]
	    Resume the specified job(s) in the foreground.  If no jobs are specified, %+ is
	    assumed.  See Job control below for more information.

     getopts optstring name [arg ...]
	    Used by shell procedures to parse the specified arguments (or positional parameters,
	    if no arguments are given) and to check for legal options.	optstring contains the
	    option letters that getopts is to recognise.  If a letter is followed by a colon, the
	    option is expected to have an argument.  Options that do not take arguments may be
	    grouped in a single argument.  If an option takes an argument and the option charac-
	    ter is not the last character of the argument it is found in, the remainder of the
	    argument is taken to be the option's argument; otherwise, the next argument is the
	    option's argument.

	    Each time getopts is invoked, it places the next option in the shell parameter name
	    and the index of the argument to be processed by the next call to getopts in the
	    shell parameter OPTIND.  If the option was introduced with a '+', the option placed
	    in name is prefixed with a '+'.  When an option requires an argument, getopts places
	    it in the shell parameter OPTARG.

	    When an illegal option or a missing option argument is encountered, a question mark
	    or a colon is placed in name (indicating an illegal option or missing argument,
	    respectively) and OPTARG is set to the option character that caused the problem.
	    Furthermore, if optstring does not begin with a colon, a question mark is placed in
	    name, OPTARG is unset, and an error message is printed to standard error.

	    When the end of the options is encountered, getopts exits with a non-zero exit sta-
	    tus.  Options end at the first (non-option argument) argument that does not start
	    with a '-', or when a '--' argument is encountered.

	    Option parsing can be reset by setting OPTIND to 1 (this is done automatically when-
	    ever the shell or a shell procedure is invoked).

	    Warning: Changing the value of the shell parameter OPTIND to a value other than 1, or
	    parsing different sets of arguments without resetting OPTIND, may lead to unexpected

     global ...
	    See typeset.

     hash [-r] [name ...]
	    Without arguments, any hashed executable command pathnames are listed.  The -r option
	    causes all hashed commands to be removed from the hash table.  Each name is searched
	    as if it were a command name and added to the hash table if it is an executable com-

     jobs [-lnp] [job ...]
	    Display information about the specified job(s); if no jobs are specified, all jobs
	    are displayed.  The -n option causes information to be displayed only for jobs that
	    have changed state since the last notification.  If the -l option is used, the
	    process ID of each process in a job is also listed.  The -p option causes only the
	    process group of each job to be printed.  See Job control below for the format of job
	    and the displayed job.

     kill [-s signame | -signum | -signame] { job | pid | pgrp } ...
	    Send the specified signal to the specified jobs, process IDs, or process groups.  If
	    no signal is specified, the TERM signal is sent.  If a job is specified, the signal
	    is sent to the job's process group.  See Job control below for the format of job.

     kill -l [exit-status ...]
	    Print the signal name corresponding to exit-status.  If no arguments are specified, a
	    list of all the signals, their numbers, and a short description of them are printed.

     let [expression ...]
	    Each expression is evaluated (see Arithmetic expressions above).  If all expressions
	    are successfully evaluated, the exit status is 0 (1) if the last expression evaluated
	    to non-zero (zero).  If an error occurs during the parsing or evaluation of an
	    expression, the exit status is greater than 1.  Since expressions may need to be
	    quoted, (( expr )) is syntactic sugar for let "expr".

     let]   Internally used alias for let.

     mknod [-m mode] name b|c major minor
     mknod [-m mode] name p
	    Create a device special file.  The file type may be b (block type device), c (charac-
	    ter type device), or p (named pipe, FIFO).	The file created may be modified accord-
	    ing to its mode (via the -m option), major (major device number), and minor (minor
	    device number).

	    See mknod(8) for further information.

     print [-nprsu[n] | -R [-en]] [argument ...]
	    print prints its arguments on the standard output, separated by spaces and terminated
	    with a newline.  The -n option suppresses the newline.  By default, certain C escapes
	    are translated.  These include these mentioned in Backslash expansion above, as well
	    as '\c', which is equivalent to using the -n option.  Backslash expansion may be
	    inhibited with the -r option.  The -s option prints to the history file instead of
	    standard output; the -u option prints to file descriptor n (n defaults to 1 if
	    omitted); and the -p option prints to the co-process (see Co-processes above).

	    The -R option is used to emulate, to some degree, the BSD echo(1) command which does
	    not process '\' sequences unless the -e option is given.  As above, the -n option
	    suppresses the trailing newline.

     printf format [arguments ...]
	    Formatted output.  Approximately the same as the printf(1), utility, except it uses
	    the same Backslash expansion and I/O code and does hot handle floating point as the
	    rest of mksh.  This is not normally part of mksh; however, distributors may have
	    added this as builtin as a speed hack.  Do not use in new code.

     pwd [-LP]
	    Print the present working directory.  If the -L option is used or if the physical
	    option isn't set (see the set command below), the logical path is printed (i.e. the
	    path used to cd to the current directory).	If the -P option (physical path) is used
	    or if the physical option is set, the path determined from the filesystem (by follow-
	    ing '..' directories to the root directory) is printed.

     read [-A | -a] [-d x] [-N z | -n z] [-p | -u[n]] [-t n] [-rs] [p ...]
	    Reads a line of input, separates the input into fields using the IFS parameter (see
	    Substitution above), and assigns each field to the specified parameters p.	If no
	    parameters are specified, the REPLY parameter is used to store the result.	With the
	    -A and -a options, only no or one parameter is accepted.  If there are more parame-
	    ters than fields, the extra parameters are set to the empty string or 0; if there are
	    more fields than parameters, the last parameter is assigned the remaining fields
	    (including the word separators).

	    The options are as follows:

	    -A	   Store the result into the parameter p (or REPLY) as array of words.

	    -a	   Store the result without word splitting into the parameter p (or REPLY) as
		   array of characters (wide characters if the utf8-mode option is enacted,
		   octets otherwise).

	    -d x   Use the first byte of x, NUL if empty, instead of the ASCII newline character
		   as input line delimiter.

	    -N z   Instead of reading till end-of-line, read exactly z bytes; less if EOF or a
		   timeout occurs.

	    -n z   Instead of reading till end-of-line, read up to z bytes but return as soon as
		   any bytes are read, e.g. from a slow terminal device, or if EOF or a timeout

	    -p	   Read from the currently active co-process, see Co-processes above for details
		   on this.

	    -u[n]  Read from the file descriptor n (defaults to 0, i.e. standard input).  The
		   argument must immediately follow the option character.

	    -t n   Interrupt reading after n seconds (specified as positive decimal value with an
		   optional fractional part).

	    -r	   Normally, the ASCII backslash character escapes the special meaning of the
		   following character and is stripped from the input; read does not stop when
		   encountering a backslash-newline sequence and does not store that newline in
		   the result.	This option enables raw mode, in which backslashes are not pro-

	    -s	   The input line is saved to the history.

	    If the input is a terminal, both the -N and -n options set it into raw mode; they
	    read an entire file if -1 is passed as z argument.

	    The first parameter may have a question mark and a string appended to it, in which
	    case the string is used as a prompt (printed to standard error before any input is
	    read) if the input is a tty(4) (e.g. read nfoo?'number of foos: ').

	    If no input is read or a timeout occurred, read exits with a non-zero status.

	    Another handy set of tricks: If read is run in a loop such as while read foo; do ...;
	    done then leading whitespace will be removed (IFS) and backslashes processed.  You
	    might want to use while IFS= read -r foo; do ...; done for pristine I/O.  Similarily,
	    when using the -a option, use of the -r option might be prudent; the same applies

		  find . -type f -print0 | \
		      while IFS= read -d '' -r filename; do
			  print -r -- "found <${filename#./}>"

	    The inner loop will be executed in a subshell and variable changes cannot be propa-
	    gated if executed in a pipeline:

		  bar | baz | while read foo; do ...; done

	    Use co-processes instead:

		  bar | baz |&
		  while read -p foo; do ...; done
		  exec 3>&p; exec 3>&-

     readonly [-p] [parameter [=value] ...]
	    Sets the read-only attribute of the named parameters.  If values are given, parame-
	    ters are set to them before setting the attribute.	Once a parameter is made read-
	    only, it cannot be unset and its value cannot be changed.

	    If no parameters are specified, the names of all parameters with the read-only
	    attribute are printed one per line, unless the -p option is used, in which case
	    readonly commands defining all read-only parameters, including their values, are

     realpath [--] name
	    Prints the resolved absolute pathname corresponding to name.  If name ends with a
	    slash ('/'), it's also checked for existence and whether it is a directory; other-
	    wise, realpath returns 0 if the pathname either exists or can be created immediately,
	    i.e. all but the last component exist and are directories.

     rename [--] from to
	    Renames the file from to to.  Both must be complete pathnames and on the same device.
	    This builtin is intended for emergency situations where /bin/mv becomes unusable, and
	    directly calls rename(2).

     return [status]
	    Returns from a function or . script, with exit status status.  If no status is given,
	    the exit status of the last executed command is used.  If used outside of a function
	    or . script, it has the same effect as exit.  Note that mksh treats both profile and
	    ENV files as . scripts, while the original Korn shell only treats profiles as .

     set [+-abCefhiklmnprsUuvXx] [+-o option] [+-A name] [--] [arg ...]
	    The set command can be used to set (-) or clear (+) shell options, set the positional
	    parameters, or set an array parameter.  Options can be changed using the +-o option
	    syntax, where option is the long name of an option, or using the +-letter syntax,
	    where letter is the option's single letter name (not all options have a single letter
	    name).  The following table lists both option letters (if they exist) and long names
	    along with a description of what the option does:

	    -A name
		 Sets the elements of the array parameter name to arg ... If -A is used, the
		 array is reset (i.e. emptied) first; if +A is used, the first N elements are set
		 (where N is the number of arguments); the rest are left untouched.

		 An alternative syntax for the command set -A foo -- a b c which is compatible to
		 GNU bash and also supported by AT&T UNIX ksh93 is: foo=(a b c); foo+=(d e)

		 Another AT&T UNIX ksh93 and GNU bash extension allows specifying the indices
		 used for arg ... (from the above example, a b c) like this: set -A foo -- [0]=a
		 [1]=b [2]=c or foo=([0]=a [1]=b [2]=c) which can also be written foo=([0]=a b c)
		 because indices are incremented automatically.

	    -a | -o allexport
		 All new parameters are created with the export attribute.

	    -b | -o notify
		 Print job notification messages asynchronously, instead of just before the
		 prompt.  Only used if job control is enabled (-m).

	    -C | -o noclobber
		 Prevent > redirection from overwriting existing files.  Instead, >| must be used
		 to force an overwrite.

	    -e | -o errexit
		 Exit (after executing the ERR trap) as soon as an error occurs or a command
		 fails (i.e. exits with a non-zero status).  This does not apply to commands
		 whose exit status is explicitly tested by a shell construct such as if, until,
		 while, &&, ||, or ! statements.

	    -f | -o noglob
		 Do not expand file name patterns.

	    -h | -o trackall
		 Create tracked aliases for all executed commands (see Aliases above).	Enabled
		 by default for non-interactive shells.

	    -i | -o interactive
		 The shell is an interactive shell.  This option can only be used when the shell
		 is invoked.  See above for a description of what this means.

	    -k | -o keyword
		 Parameter assignments are recognised anywhere in a command.

	    -l | -o login
		 The shell is a login shell.  This option can only be used when the shell is
		 invoked.  See above for a description of what this means.

	    -m | -o monitor
		 Enable job control (default for interactive shells).

	    -n | -o noexec
		 Do not execute any commands.  Useful for checking the syntax of scripts (ignored
		 if interactive).

	    -p | -o privileged
		 The shell is a privileged shell.  It is set automatically if, when the shell
		 starts, the real UID or GID does not match the effective UID (EUID) or GID
		 (EGID), respectively.	See above for a description of what this means.

	    -r | -o restricted
		 The shell is a restricted shell.  This option can only be used when the shell is
		 invoked.  See above for a description of what this means.

	    -s | -o stdin
		 If used when the shell is invoked, commands are read from standard input.  Set
		 automatically if the shell is invoked with no arguments.

		 When -s is used with the set command it causes the specified arguments to be
		 sorted before assigning them to the positional parameters (or to array name, if
		 -A is used).

	    -U | -o utf8-mode
		 Enable UTF-8 support in the Emacs editing mode and internal string handling
		 functions.  This flag is disabled by default, but can be enabled by setting it
		 on the shell command line; is enabled automatically for interactive shells if
		 requested at compile time, your system supports setlocale(LC_CTYPE, "") and
		 optionally nl_langinfo(CODESET), or the LC_ALL, LC_CTYPE, or LANG environment
		 variables, and at least one of these returns something that matches ``UTF-8'' or
		 ``utf8'' case-insensitively; for direct builtin calls depending on the aforemen-
		 tioned environment variables; or for stdin or scripts, if the input begins with
		 a UTF-8 Byte Order Mark.

	    -u | -o nounset
		 Referencing of an unset parameter, other than ``$@'' or ``$*'', is treated as an
		 error, unless one of the '-', '+', or '=' modifiers is used.

	    -v | -o verbose
		 Write shell input to standard error as it is read.

	    -X | -o markdirs
		 Mark directories with a trailing '/' during file name generation.

	    -x | -o xtrace
		 Print command trees when they are executed, preceded by the value of PS4.

	    -o bgnice
		 Background jobs are run with lower priority.

	    -o braceexpand
		 Enable brace expansion (a.k.a. alternation).  This is enabled by default.  If
		 disabled, tilde expansion after an equals sign is disabled as a side effect.

	    -o emacs
		 Enable BRL emacs-like command-line editing (interactive shells only); see Emacs
		 editing mode.

	    -o gmacs
		 Enable gmacs-like command-line editing (interactive shells only).  Currently
		 identical to emacs editing except that transpose-chars (^T) acts slightly dif-

	    -o ignoreeof
		 The shell will not (easily) exit when end-of-file is read; exit must be used.
		 To avoid infinite loops, the shell will exit if EOF is read 13 times in a row.

	    -o nohup
		 Do not kill running jobs with a SIGHUP signal when a login shell exits.  Cur-
		 rently set by default, but this may change in the future to be compatible with
		 AT&T UNIX ksh, which doesn't have this option, but does send the SIGHUP signal.

	    -o nolog
		 No effect.  In the original Korn shell, this prevents function definitions from
		 being stored in the history file.

	    -o physical
		 Causes the cd and pwd commands to use ``physical'' (i.e. the filesystem's) '..'
		 directories instead of ``logical'' directories (i.e. the shell handles '..',
		 which allows the user to be oblivious of symbolic links to directories).  Clear
		 by default.  Note that setting this option does not affect the current value of
		 the PWD parameter; only the cd command changes PWD.  See the cd and pwd commands
		 above for more details.

	    -o pipefail
		 Make the exit status of a pipeline (before logically complementing) the right-
		 most non-zero errorlevel, or zero if all commands exited with zero.

	    -o posix
		 Enable a somewhat more POSIXish mode.	As a side effect, setting this flag turns
		 off braceexpand mode, which can be turned back on manually, and sh mode.

	    -o sh
		 Enable /bin/sh (kludge) mode.	Automatically enabled if the basename of the
		 shell invocation begins with ``sh'' and this autodetection feature is compiled
		 in (not in MirBSD).  As a side effect, setting this flag turns off braceexpand
		 mode, which can be turned back on manually, and posix mode.

	    -o vi
		 Enable vi(1)-like command-line editing (interactive shells only).

	    -o vi-esccomplete
		 In vi command-line editing, do command and file name completion when escape (^[)
		 is entered in command mode.

	    -o vi-tabcomplete
		 In vi command-line editing, do command and file name completion when tab (^I) is
		 entered in insert mode.  This is the default.

	    -o viraw
		 No effect.  In the original Korn shell, unless viraw was set, the vi command-
		 line mode would let the tty(4) driver do the work until ESC (^[) was entered.
		 mksh is always in viraw mode.

	    These options can also be used upon invocation of the shell.  The current set of
	    options (with single letter names) can be found in the parameter '$-'.  set -o with
	    no option name will list all the options and whether each is on or off; set +o will
	    print the long names of all options that are currently on.

	    Remaining arguments, if any, are positional parameters and are assigned, in order, to
	    the positional parameters (i.e. $1, $2, etc.).  If options end with '--' and there
	    are no remaining arguments, all positional parameters are cleared.	If no options or
	    arguments are given, the values of all names are printed.  For unknown historical
	    reasons, a lone '-' option is treated specially - it clears both the -v and -x

     shift [number]
	    The positional parameters number+1, number+2, etc. are renamed to '1', '2', etc.
	    number defaults to 1.

     sleep seconds
	    Suspends execution for a minimum of the seconds specified as positive decimal value
	    with an optional fractional part.  Signal delivery may continue execution earlier.

     source file [arg ...]
	    Like . (``dot''), except that the current working directory is appended to the PATH
	    in GNU bash and mksh.  In ksh93 and mksh, this is implemented as a shell alias
	    instead of a builtin.

     test expression
     [ expression ]
	    test evaluates the expression and returns zero status if true, 1 if false, or greater
	    than 1 if there was an error.  It is normally used as the condition command of if and
	    while statements.  Symbolic links are followed for all file expressions except -h and

	    The following basic expressions are available:

	    -a file	       file exists.

	    -b file	       file is a block special device.

	    -c file	       file is a character special device.

	    -d file	       file is a directory.

	    -e file	       file exists.

	    -f file	       file is a regular file.

	    -G file	       file's group is the shell's effective group ID.

	    -g file	       file's mode has the setgid bit set.

	    -H file	       file is a context dependent directory (only useful on HP-UX).

	    -h file	       file is a symbolic link.

	    -k file	       file's mode has the sticky(8) bit set.

	    -L file	       file is a symbolic link.

	    -O file	       file's owner is the shell's effective user ID.

	    -o option	       Shell option is set (see the set command above for a list of
			       options).  As a non-standard extension, if the option starts with
			       a '!', the test is negated; the test always fails if option
			       doesn't exist (so [ -o foo -o -o !foo ] returns true if and only
			       if option foo exists).  The same can be achieved with [ -o ?foo ]
			       like in AT&T UNIX ksh93.  option can also be the short flag led by
			       either '-' or '+' (no logical negation), for example '-x' or '+x'
			       instead of 'xtrace'.

	    -p file	       file is a named pipe (FIFO).

	    -r file	       file exists and is readable.

	    -S file	       file is a unix(4)-domain socket.

	    -s file	       file is not empty.

	    -t fd	       File descriptor fd is a tty(4) device.

	    -u file	       file's mode has the setuid bit set.

	    -w file	       file exists and is writable.

	    -x file	       file exists and is executable.

	    file1 -nt file2    file1 is newer than file2 or file1 exists and file2 does not.

	    file1 -ot file2    file1 is older than file2 or file2 exists and file1 does not.

	    file1 -ef file2    file1 is the same file as file2.

	    string	       string has non-zero length.

	    -n string	       string is not empty.

	    -z string	       string is empty.

	    string = string    Strings are equal.

	    string == string   Strings are equal.

	    string > string    First string operand is greater than second string operand.

	    string < string    First string operand is less than second string operand.

	    string != string   Strings are not equal.

	    number -eq number  Numbers compare equal.

	    number -ne number  Numbers compare not equal.

	    number -ge number  Numbers compare greater than or equal.

	    number -gt number  Numbers compare greater than.

	    number -le number  Numbers compare less than or equal.

	    number -lt number  Numbers compare less than.

	    The above basic expressions, in which unary operators have precedence over binary
	    operators, may be combined with the following operators (listed in increasing order
	    of precedence):

		  expr -o expr		  Logical OR.
		  expr -a expr		  Logical AND.
		  ! expr		  Logical NOT.
		  ( expr )		  Grouping.

	    Note that a number actually may be an arithmetic expression, such as a mathematical
	    term or the name of an integer variable:

		  x=1; [ "x" -eq 1 ]	  evaluates to true

	    Note that some special rules are applied (courtesy of POSIX) if the number of argu-
	    ments to test or inside the brackets [ ... ] is less than five: if leading '!' argu-
	    ments can be stripped such that only one to three arguments remain, then the lowered
	    comparison is executed; (thanks to XSI) parentheses \( ... \) lower four- and three-
	    argument forms to two- and one-argument forms, respectively; three-argument forms
	    ultimately prefer binary operations, followed by negation and parenthesis lowering;
	    two- and four-argument forms prefer negation followed by parenthesis; the one-argu-
	    ment form always implies -n.

	    Note: A common mistake is to use ``if [ $foo = bar ]'' which fails if parameter
	    ``foo'' is NULL or unset, if it has embedded spaces (i.e. IFS octets), or if it is a
	    unary operator like '!' or '-n'.  Use tests like ``if [ x"$foo" = x"bar" ]'' instead,
	    or the double-bracket operator ``if [[ $foo = bar ]]'' or, to avoid pattern matching
	    (see [[ above): ``if [[ $foo = "$bar" ]]''

	    The [[ ... ]] construct is not only more secure to use but also often faster.

     time [-p] [pipeline]
	    If a pipeline is given, the times used to execute the pipeline are reported.  If no
	    pipeline is given, then the user and system time used by the shell itself, and all
	    the commands it has run since it was started, are reported.  The times reported are
	    the real time (elapsed time from start to finish), the user CPU time (time spent run-
	    ning in user mode), and the system CPU time (time spent running in kernel mode).
	    Times are reported to standard error; the format of the output is:

		  0m0.00s real	   0m0.00s user     0m0.00s system

	    If the -p option is given the output is slightly longer:

		  real	   0.00
		  user	   0.00
		  sys	   0.00

	    It is an error to specify the -p option unless pipeline is a simple command.

	    Simple redirections of standard error do not affect the output of the time command:

		  $ time sleep 1 2>afile
		  $ { time sleep 1; } 2>afile

	    Times for the first command do not go to ``afile'', but those of the second command

     times  Print the accumulated user and system times used both by the shell and by processes
	    that the shell started which have exited.  The format of the output is:

		  0m0.00s 0m0.00s
		  0m0.00s 0m0.00s

     trap [handler signal ...]
	    Sets a trap handler that is to be executed when any of the specified signals are
	    received.  handler is either a NULL string, indicating the signals are to be ignored,
	    a minus sign ('-'), indicating that the default action is to be taken for the signals
	    (see signal(3)), or a string containing shell commands to be evaluated and executed
	    at the first opportunity (i.e. when the current command completes, or before printing
	    the next PS1 prompt) after receipt of one of the signals.  signal is the name of a
	    signal (e.g. PIPE or ALRM) or the number of the signal (see the kill -l command

	    There are two special signals: EXIT (also known as 0) which is executed when the
	    shell is about to exit, and ERR, which is executed after an error occurs (an error is
	    something that would cause the shell to exit if the -e or errexit option were set -
	    see the set command above).  EXIT handlers are executed in the environment of the
	    last executed command.  Note that for non-interactive shells, the trap handler cannot
	    be changed for signals that were ignored when the shell started.

	    With no arguments, trap lists, as a series of trap commands, the current state of the
	    traps that have been set since the shell started.  Note that the output of trap can-
	    not be usefully piped to another process (an artifact of the fact that traps are
	    cleared when subprocesses are created).

	    The original Korn shell's DEBUG trap and the handling of ERR and EXIT traps in func-
	    tions are not yet implemented.

     true   A command that exits with a zero value.

     global [[+-alpnrtUux] [-L[n]] [-R[n]] [-Z[n]] [-i[n]] | -f [-tux]] [name [=value] ...]
     typeset [[+-alpnrtUux] [-LRZ[n]] [-i[n]] | -f [-tux]] [name [=value] ...]
	    Display or set parameter attributes.  With no name arguments, parameter attributes
	    are displayed; if no options are used, the current attributes of all parameters are
	    printed as typeset commands; if an option is given (or '-' with no option letter),
	    all parameters and their values with the specified attributes are printed; if options
	    are introduced with '+', parameter values are not printed.

	    If name arguments are given, the attributes of the named parameters are set (-) or
	    cleared (+).  Values for parameters may optionally be specified.  For name[*], the
	    change affects the entire array, and no value may be specified.

	    If typeset is used inside a function, any parameters specified are localised.  This
	    is not done by the otherwise identical global.  Note: This means that mksh 's global
	    command is not equivalent to other programming languages' as it does not allow a
	    function called from another function to access a parameter at truly global scope,
	    but only prevents putting an accessed one into local scope.

	    When -f is used, typeset operates on the attributes of functions.  As with parame-
	    ters, if no name arguments are given, functions are listed with their values (i.e.
	    definitions) unless options are introduced with '+', in which case only the function
	    names are reported.

	    -a	    Indexed array attribute.

	    -f	    Function mode.  Display or set functions and their attributes, instead of

	    -i[n]   Integer attribute.	n specifies the base to use when displaying the integer
		    (if not specified, the base given in the first assignment is used).  Parame-
		    ters with this attribute may be assigned values containing arithmetic expres-

	    -L[n]   Left justify attribute.  n specifies the field width.  If n is not specified,
		    the current width of a parameter (or the width of its first assigned value)
		    is used.  Leading whitespace (and zeros, if used with the -Z option) is
		    stripped.  If necessary, values are either truncated or space padded to fit
		    the field width.

	    -l	    Lower case attribute.  All upper case characters in values are converted to
		    lower case.  (In the original Korn shell, this parameter meant ``long
		    integer'' when used with the -i option.)

	    -n	    Create a bound variable (name reference): any access to the variable name
		    will access the variable value in the current scope (this is different from
		    AT&T UNIX ksh93!)  instead.  Also different from AT&T UNIX ksh93 is that
		    value is lazily evaluated at the time name is accessed.  This can be used by
		    functions to access variables whose names are passed as parametres, instead
		    of using eval.

	    -p	    Print complete typeset commands that can be used to re-create the attributes
		    and values of parameters.

	    -R[n]   Right justify attribute.  n specifies the field width.  If n is not speci-
		    fied, the current width of a parameter (or the width of its first assigned
		    value) is used.  Trailing whitespace is stripped.  If necessary, values are
		    either stripped of leading characters or space padded to make them fit the
		    field width.

	    -r	    Read-only attribute.  Parameters with this attribute may not be assigned to
		    or unset.  Once this attribute is set, it cannot be turned off.

	    -t	    Tag attribute.  Has no meaning to the shell; provided for application use.

		    For functions, -t is the trace attribute.  When functions with the trace
		    attribute are executed, the xtrace (-x) shell option is temporarily turned

	    -U	    Unsigned integer attribute.  Integers are printed as unsigned values (combine
		    with the -i option).  This option is not in the original Korn shell.

	    -u	    Upper case attribute.  All lower case characters in values are converted to
		    upper case.  (In the original Korn shell, this parameter meant ``unsigned
		    integer'' when used with the -i option which meant upper case letters would
		    never be used for bases greater than 10.  See the -U option.)

		    For functions, -u is the undefined attribute.  See Functions above for the
		    implications of this.

	    -x	    Export attribute.  Parameters (or functions) are placed in the environment of
		    any executed commands.  Exported functions are not yet implemented.

	    -Z[n]   Zero fill attribute.  If not combined with -L, this is the same as -R, except
		    zero padding is used instead of space padding.  For integers, the number
		    instead of the base is padded.

	    If any of the -i, -L, -l, -R, -U, -u, or -Z options are changed, all others from this
	    set are cleared, unless they are also given on the same command line.

     ulimit [-aBCcdefHiLlMmnOPpqrSsTtVvw] [value]
	    Display or set process limits.  If no options are used, the file size limit (-f) is
	    assumed.  value, if specified, may be either an arithmetic expression or the word
	    ``unlimited''.  The limits affect the shell and any processes created by the shell
	    after a limit is imposed.  Note that some systems may not allow limits to be
	    increased once they are set.  Also note that the types of limits available are system
	    dependent - some systems have only the -f limit.

	    -a	   Display all limits; unless -H is used, soft limits are displayed.

	    -B n   Set the socket buffer size to n kibibytes.

	    -C n   Set the number of cached threads to n.

	    -c n   Impose a size limit of n blocks on the size of core dumps.

	    -d n   Impose a size limit of n kibibytes on the size of the data area.

	    -e n   Set the maximum niceness to n.

	    -f n   Impose a size limit of n blocks on files written by the shell and its child
		   processes (files of any size may be read).

	    -H	   Set the hard limit only (the default is to set both hard and soft limits).

	    -i n   Set the number of pending signals to n.

	    -L n   Control flocks; documentation is missing.

	    -l n   Impose a limit of n kibibytes on the amount of locked (wired) physical memory.

	    -M n   Set the AIO locked memory to n kibibytes.

	    -m n   Impose a limit of n kibibytes on the amount of physical memory used.

	    -n n   Impose a limit of n file descriptors that can be open at once.

	    -O n   Set the number of AIO operations to n.

	    -P n   Limit the number of threads per process to n.

	    -p n   Impose a limit of n processes that can be run by the user at any one time.

	    -q n   Limit the size of POSIX message queues to n bytes.

	    -r n   Set the maximum real-time priority to n.

	    -S	   Set the soft limit only (the default is to set both hard and soft limits).

	    -s n   Impose a size limit of n kibibytes on the size of the stack area.

	    -T n   Impose a time limit of n real seconds to be used by each process.

	    -t n   Impose a time limit of n CPU seconds spent in user mode to be used by each

	    -V n   Set the number of vnode monitors on Haiku to n.

	    -v n   Impose a limit of n kibibytes on the amount of virtual memory (address space)

	    -w n   Impose a limit of n kibibytes on the amount of swap space used.

	    As far as ulimit is concerned, a block is 512 bytes.

     umask [-S] [mask]
	    Display or set the file permission creation mask, or umask (see umask(2)).	If the -S
	    option is used, the mask displayed or set is symbolic; otherwise, it is an octal num-

	    Symbolic masks are like those used by chmod(1).  When used, they describe what per-
	    missions may be made available (as opposed to octal masks in which a set bit means
	    the corresponding bit is to be cleared).  For example, ``ug=rwx,o='' sets the mask so
	    files will not be readable, writable, or executable by ``others'', and is equivalent
	    (on most systems) to the octal mask ``007''.

     unalias [-adt] [name ...]
	    The aliases for the given names are removed.  If the -a option is used, all aliases
	    are removed.  If the -t or -d options are used, the indicated operations are carried
	    out on tracked or directory aliases, respectively.

     unset [-fv] parameter ...
	    Unset the named parameters (-v, the default) or functions (-f).  With parameter[*],
	    attributes are kept, only values are unset.

	    The exit status is non-zero if any of the parameters have the read-only attribute
	    set, zero otherwise.

     wait [job ...]
	    Wait for the specified job(s) to finish.  The exit status of wait is that of the last
	    specified job; if the last job is killed by a signal, the exit status is 128 + the
	    number of the signal (see kill -l exit-status above); if the last specified job can't
	    be found (because it never existed, or had already finished), the exit status of wait
	    is 127.  See Job control below for the format of job.  wait will return if a signal
	    for which a trap has been set is received, or if a SIGHUP, SIGINT, or SIGQUIT signal
	    is received.

	    If no jobs are specified, wait waits for all currently running jobs (if any) to fin-
	    ish and exits with a zero status.  If job monitoring is enabled, the completion sta-
	    tus of jobs is printed (this is not the case when jobs are explicitly specified).

     whence [-pv] [name ...]
	    For each name, the type of command is listed (reserved word, built-in, alias, func-
	    tion, tracked alias, or executable).  If the -p option is used, a path search is per-
	    formed even if name is a reserved word, alias, etc.  Without the -v option, whence is
	    similar to command -v except that whence will find reserved words and won't print
	    aliases as alias commands.	With the -v option, whence is the same as command -V.
	    Note that for whence, the -p option does not affect the search path used, as it does
	    for command.  If the type of one or more of the names could not be determined, the
	    exit status is non-zero.

   Job control
     Job control refers to the shell's ability to monitor and control jobs which are processes or
     groups of processes created for commands or pipelines.  At a minimum, the shell keeps track
     of the status of the background (i.e. asynchronous) jobs that currently exist; this informa-
     tion can be displayed using the jobs commands.  If job control is fully enabled (using set
     -m or set -o monitor), as it is for interactive shells, the processes of a job are placed in
     their own process group.  Foreground jobs can be stopped by typing the suspend character
     from the terminal (normally ^Z), jobs can be restarted in either the foreground or back-
     ground using the fg and bg commands, and the state of the terminal is saved or restored when
     a foreground job is stopped or restarted, respectively.

     Note that only commands that create processes (e.g. asynchronous commands, subshell com-
     mands, and non-built-in, non-function commands) can be stopped; commands like read cannot

     When a job is created, it is assigned a job number.  For interactive shells, this number is
     printed inside ``[..]'', followed by the process IDs of the processes in the job when an
     asynchronous command is run.  A job may be referred to in the bg, fg, jobs, kill, and wait
     commands either by the process ID of the last process in the command pipeline (as stored in
     the $! parameter) or by prefixing the job number with a percent sign ('%').  Other percent
     sequences can also be used to refer to jobs:

     %+ | %% | %    The most recently stopped job, or, if there are no stopped jobs, the oldest
		    running job.

     %- 	    The job that would be the %+ job if the latter did not exist.

     %n 	    The job with job number n.

     %?string	    The job with its command containing the string string (an error occurs if
		    multiple jobs are matched).

     %string	    The job with its command starting with the string string (an error occurs if
		    multiple jobs are matched).

     When a job changes state (e.g. a background job finishes or foreground job is stopped), the
     shell prints the following status information:

	   [number] flag status command


     number   is the job number of the job;

     flag     is the '+' or '-' character if the job is the %+ or %- job, respectively, or space
	      if it is neither;

     status   indicates the current state of the job and can be:

	      Done [number]
			 The job exited.  number is the exit status of the job which is omitted
			 if the status is zero.

	      Running	 The job has neither stopped nor exited (note that running does not nec-
			 essarily mean consuming CPU time - the process could be blocked waiting
			 for some event).

	      Stopped [signal]
			 The job was stopped by the indicated signal (if no signal is given, the
			 job was stopped by SIGTSTP).

	      signal-description [``core dumped'']
			 The job was killed by a signal (e.g. memory fault, hangup); use kill -l
			 for a list of signal descriptions.  The ``core dumped'' message indi-
			 cates the process created a core file.

     command  is the command that created the process.	If there are multiple processes in the
	      job, each process will have a line showing its command and possibly its status, if
	      it is different from the status of the previous process.

     When an attempt is made to exit the shell while there are jobs in the stopped state, the
     shell warns the user that there are stopped jobs and does not exit.  If another attempt is
     immediately made to exit the shell, the stopped jobs are sent a SIGHUP signal and the shell
     exits.  Similarly, if the nohup option is not set and there are running jobs when an attempt
     is made to exit a login shell, the shell warns the user and does not exit.  If another
     attempt is immediately made to exit the shell, the running jobs are sent a SIGHUP signal and
     the shell exits.

   Interactive input line editing
     The shell supports three modes of reading command lines from a tty(4) in an interactive ses-
     sion, controlled by the emacs, gmacs, and vi options (at most one of these can be set at
     once).  The default is emacs.  Editing modes can be set explicitly using the set built-in.
     If none of these options are enabled, the shell simply reads lines using the normal tty(4)
     driver.  If the emacs or gmacs option is set, the shell allows emacs-like editing of the
     command; similarly, if the vi option is set, the shell allows vi-like editing of the com-
     mand.  These modes are described in detail in the following sections.

     In these editing modes, if a line is longer than the screen width (see the COLUMNS parame-
     ter), a '>', '+', or '<' character is displayed in the last column indicating that there are
     more characters after, before and after, or before the current position, respectively.  The
     line is scrolled horizontally as necessary.

     Completed lines are pushed into the history, unless they begin with an IFS octet or IFS
     white space, or are the same as the previous line.

   Emacs editing mode
     When the emacs option is set, interactive input line editing is enabled.  Warning: This mode
     is slightly different from the emacs mode in the original Korn shell.  In this mode, various
     editing commands (typically bound to one or more control characters) cause immediate actions
     without waiting for a newline.  Several editing commands are bound to particular control
     characters when the shell is invoked; these bindings can be changed using the bind command.

     The following is a list of available editing commands.  Each description starts with the
     name of the command, suffixed with a colon; an [n] (if the command can be prefixed with a
     count); and any keys the command is bound to by default, written using caret notation e.g.
     the ASCII ESC character is written as ^[.	These control sequences are not case sensitive.
     A count prefix for a command is entered using the sequence ^[n, where n is a sequence of 1
     or more digits.  Unless otherwise specified, if a count is omitted, it defaults to 1.

     Note that editing command names are used only with the bind command.  Furthermore, many
     editing commands are useful only on terminals with a visible cursor.  The default bindings
     were chosen to resemble corresponding Emacs key bindings.	The user's tty(4) characters
     (e.g. ERASE) are bound to reasonable substitutes and override the default bindings.

     abort: ^C, ^G
	     Abort the current command, empty the line buffer and set the exit state to inter-

     auto-insert: [n]
	     Simply causes the character to appear as literal input.  Most ordinary characters
	     are bound to this.

     backward-char: [n] ^B, ^XD, ANSI-CurLeft
	     Moves the cursor backward n characters.

     backward-word: [n] ^[b, ANSI-Ctrl-CurLeft, ANSI-Alt-CurLeft
	     Moves the cursor backward to the beginning of the word; words consist of alphanumer-
	     ics, underscore ('_'), and dollar sign ('$') characters.

     beginning-of-history: ^[<
	     Moves to the beginning of the history.

     beginning-of-line: ^A, ANSI-Home
	     Moves the cursor to the beginning of the edited input line.

     capitalise-word: [n] ^[C, ^[c
	     Uppercase the first character in the next n words, leaving the cursor past the end
	     of the last word.

     clear-screen: ^[^L
	     Prints a compile-time configurable sequence to clear the screen and home the cursor,
	     redraws the entire prompt and the currently edited input line.  The default sequence
	     works for almost all standard terminals.

     comment: ^[#
	     If the current line does not begin with a comment character, one is added at the
	     beginning of the line and the line is entered (as if return had been pressed); oth-
	     erwise, the existing comment characters are removed and the cursor is placed at the
	     beginning of the line.

     complete: ^[^[
	     Automatically completes as much as is unique of the command name or the file name
	     containing the cursor.  If the entire remaining command or file name is unique, a
	     space is printed after its completion, unless it is a directory name in which case
	     '/' is appended.  If there is no command or file name with the current partial word
	     as its prefix, a bell character is output (usually causing a beep to be sounded).

     complete-command: ^X^[
	     Automatically completes as much as is unique of the command name having the partial
	     word up to the cursor as its prefix, as in the complete command above.

     complete-file: ^[^X
	     Automatically completes as much as is unique of the file name having the partial
	     word up to the cursor as its prefix, as in the complete command described above.

     complete-list: ^I, ^[=
	     Complete as much as is possible of the current word, and list the possible comple-
	     tions for it.  If only one completion is possible, match as in the complete command
	     above.  Note that ^I is usually generated by the TAB (tabulator) key.

     delete-char-backward: [n] ERASE, ^?, ^H
	     Deletes n characters before the cursor.

     delete-char-forward: [n] ANSI-Del
	     Deletes n characters after the cursor.

     delete-word-backward: [n] WERASE, ^[^?, ^[^H, ^[h
	     Deletes n words before the cursor.

     delete-word-forward: [n] ^[d
	     Deletes characters after the cursor up to the end of n words.

     down-history: [n] ^N, ^XB, ANSI-CurDown
	     Scrolls the history buffer forward n lines (later).  Each input line originally
	     starts just after the last entry in the history buffer, so down-history is not use-
	     ful until either search-history, search-history-up or up-history has been performed.

     downcase-word: [n] ^[L, ^[l
	     Lowercases the next n words.

     edit-line: [n] ^Xe
	     Edit line n or the current line, if not specified, interactively.	The actual com-
	     mand executed is fc -e ${VISUAL:-${EDITOR:-vi}} n.

     end-of-history: ^[>
	     Moves to the end of the history.

     end-of-line: ^E, ANSI-End
	     Moves the cursor to the end of the input line.

     eot: ^_
	     Acts as an end-of-file; this is useful because edit-mode input disables normal ter-
	     minal input canonicalization.

     eot-or-delete: [n] ^D
	     Acts as eot if alone on a line; otherwise acts as delete-char-forward.

     error: (not bound)
	     Error (ring the bell).

     exchange-point-and-mark: ^X^X
	     Places the cursor where the mark is and sets the mark to where the cursor was.

     expand-file: ^[*
	     Appends a '*' to the current word and replaces the word with the result of perform-
	     ing file globbing on the word.  If no files match the pattern, the bell is rung.

     forward-char: [n] ^F, ^XC, ANSI-CurRight
	     Moves the cursor forward n characters.

     forward-word: [n] ^[f, ANSI-Ctrl-CurRight, ANSI-Alt-CurRight
	     Moves the cursor forward to the end of the nth word.

     goto-history: [n] ^[g
	     Goes to history number n.

     kill-line: KILL
	     Deletes the entire input line.

     kill-region: ^W
	     Deletes the input between the cursor and the mark.

     kill-to-eol: [n] ^K
	     Deletes the input from the cursor to the end of the line if n is not specified; oth-
	     erwise deletes characters between the cursor and column n.

     list: ^[?
	     Prints a sorted, columnated list of command names or file names (if any) that can
	     complete the partial word containing the cursor.  Directory names have '/' appended
	     to them.

     list-command: ^X?
	     Prints a sorted, columnated list of command names (if any) that can complete the
	     partial word containing the cursor.

     list-file: ^X^Y
	     Prints a sorted, columnated list of file names (if any) that can complete the par-
	     tial word containing the cursor.  File type indicators are appended as described
	     under list above.

     newline: ^J, ^M
	     Causes the current input line to be processed by the shell.  The current cursor
	     position may be anywhere on the line.

     newline-and-next: ^O
	     Causes the current input line to be processed by the shell, and the next line from
	     history becomes the current line.	This is only useful after an up-history,
	     search-history or search-history-up.

     no-op: QUIT
	     This does nothing.

     prefix-1: ^[
	     Introduces a 2-character command sequence.

     prefix-2: ^X, ^[[, ^[O
	     Introduces a 2-character command sequence.

     prev-hist-word: [n] ^[., ^[_
	     The last word, or, if given, the nth word (zero-based) of the previous (on repeated
	     execution, second-last, third-last, etc.) command is inserted at the cursor.  Use of
	     this editing command trashes the mark.

     quote: ^^, ^V
	     The following character is taken literally rather than as an editing command.

     redraw: ^L
	     Reprints the last line of the prompt string and the current input line on a new

     search-character-backward: [n] ^[^]
	     Search backward in the current line for the nth occurrence of the next character

     search-character-forward: [n] ^]
	     Search forward in the current line for the nth occurrence of the next character

     search-history: ^R
	     Enter incremental search mode.  The internal history list is searched backwards for
	     commands matching the input.  An initial '^' in the search string anchors the
	     search.  The escape key will leave search mode.  Other commands, including sequences
	     of escape as prefix-1 followed by a prefix-1 or prefix-2 key will be executed after
	     leaving search mode.  The abort (^G) command will restore the input line before
	     search started.  Successive search-history commands continue searching backward to
	     the next previous occurrence of the pattern.  The history buffer retains only a
	     finite number of lines; the oldest are discarded as necessary.

     search-history-up: ANSI-PgUp
	     Search backwards through the history buffer for commands whose beginning match the
	     portion of the input line before the cursor.  When used on an empty line, this has
	     the same effect as up-history.

     search-history-down: ANSI-PgDn
	     Search forwards through the history buffer for commands whose beginning match the
	     portion of the input line before the cursor.  When used on an empty line, this has
	     the same effect as down-history.  This is only useful after an up-history,
	     search-history or search-history-up.

     set-mark-command: ^[<space>
	     Set the mark at the cursor position.

     transpose-chars: ^T
	     If at the end of line, or if the gmacs option is set, this exchanges the two previ-
	     ous characters; otherwise, it exchanges the previous and current characters and
	     moves the cursor one character to the right.

     up-history: [n] ^P, ^XA, ANSI-CurUp
	     Scrolls the history buffer backward n lines (earlier).

     upcase-word: [n] ^[U, ^[u
	     Uppercase the next n words.

     version: ^[^V
	     Display the version of mksh.  The current edit buffer is restored as soon as a key
	     is pressed.  The restoring keypress is processed, unless it is a space.

     yank: ^Y
	     Inserts the most recently killed text string at the current cursor position.

     yank-pop: ^[y
	     Immediately after a yank, replaces the inserted text string with the next previously
	     killed text string.

   Vi editing mode
     Note: The vi command-line editing mode is orphaned, yet still functional.

     The vi command-line editor in mksh has basically the same commands as the vi(1) editor with
     the following exceptions:

     o	 You start out in insert mode.

     o	 There are file name and command completion commands: =, \, *, ^X, ^E, ^F, and, option-
	 ally, <tab> and <esc>.

     o	 The _ command is different (in mksh, it is the last argument command; in vi(1) it goes
	 to the start of the current line).

     o	 The / and G commands move in the opposite direction to the j command.

     o	 Commands which don't make sense in a single line editor are not available (e.g. screen
	 movement commands and ex(1)-style colon (:) commands).

     Like vi(1), there are two modes: ``insert'' mode and ``command'' mode.  In insert mode, most
     characters are simply put in the buffer at the current cursor position as they are typed;
     however, some characters are treated specially.  In particular, the following characters are
     taken from current tty(4) settings (see stty(1)) and have their usual meaning (normal values
     are in parentheses): kill (^U), erase (^?), werase (^W), eof (^D), intr (^C), and quit (^\).
     In addition to the above, the following characters are also treated specially in insert

     ^E       Command and file name enumeration (see below).

     ^F       Command and file name completion (see below).  If used twice in a row, the list of
	      possible completions is displayed; if used a third time, the completion is undone.

     ^H       Erases previous character.

     ^J | ^M  End of line.  The current line is read, parsed, and executed by the shell.

     ^V       Literal next.  The next character typed is not treated specially (can be used to
	      insert the characters being described here).

     ^X       Command and file name expansion (see below).

     <esc>    Puts the editor in command mode (see below).

     <tab>    Optional file name and command completion (see ^F above), enabled with set -o

     In command mode, each character is interpreted as a command.  Characters that don't corre-
     spond to commands, are illegal combinations of commands, or are commands that can't be car-
     ried out, all cause beeps.  In the following command descriptions, an [n] indicates the com-
     mand may be prefixed by a number (e.g. 10l moves right 10 characters); if no number prefix
     is used, n is assumed to be 1 unless otherwise specified.	The term ``current position''
     refers to the position between the cursor and the character preceding the cursor.	A
     ``word'' is a sequence of letters, digits, and underscore characters or a sequence of non-
     letter, non-digit, non-underscore, and non-whitespace characters (e.g. ``ab2*&^'' contains
     two words) and a ``big-word'' is a sequence of non-whitespace characters.

     Special mksh vi commands:

     The following commands are not in, or are different from, the normal vi file editor:

     [n]_	 Insert a space followed by the nth big-word from the last command in the history
		 at the current position and enter insert mode; if n is not specified, the last
		 word is inserted.

     #		 Insert the comment character ('#') at the start of the current line and return
		 the line to the shell (equivalent to I#^J).

     [n]g	 Like G, except if n is not specified, it goes to the most recent remembered

     [n]v	 Edit line n using the vi(1) editor; if n is not specified, the current line is
		 edited.  The actual command executed is fc -e ${VISUAL:-${EDITOR:-vi}} n.

     * and ^X	 Command or file name expansion is applied to the current big-word (with an
		 appended '*' if the word contains no file globbing characters) - the big-word is
		 replaced with the resulting words.  If the current big-word is the first on the
		 line or follows one of the characters ';', '|', '&', '(', or ')', and does not
		 contain a slash ('/'), then command expansion is done; otherwise file name
		 expansion is done.  Command expansion will match the big-word against all
		 aliases, functions, and built-in commands as well as any executable files found
		 by searching the directories in the PATH parameter.  File name expansion matches
		 the big-word against the files in the current directory.  After expansion, the
		 cursor is placed just past the last word and the editor is in insert mode.

     [n]\, [n]^F, [n]<tab>, and [n]<esc>
		 Command/file name completion.	Replace the current big-word with the longest
		 unique match obtained after performing command and file name expansion.  <tab>
		 is only recognised if the vi-tabcomplete option is set, while <esc> is only
		 recognised if the vi-esccomplete option is set (see set -o).  If n is specified,
		 the nth possible completion is selected (as reported by the command/file name
		 enumeration command).

     = and ^E	 Command/file name enumeration.  List all the commands or files that match the
		 current big-word.

     ^V 	 Display the version of mksh.  The current edit buffer is restored as soon as a
		 key is pressed.  The restoring keypress is ignored.

     @c 	 Macro expansion.  Execute the commands found in the alias c.

     Intra-line movement commands:

     [n]h and [n]^H
	     Move left n characters.

     [n]l and [n]<space>
	     Move right n characters.

     0	     Move to column 0.

     ^	     Move to the first non-whitespace character.

     [n]|    Move to column n.

     $	     Move to the last character.

     [n]b    Move back n words.

     [n]B    Move back n big-words.

     [n]e    Move forward to the end of the word, n times.

     [n]E    Move forward to the end of the big-word, n times.

     [n]w    Move forward n words.

     [n]W    Move forward n big-words.

     %	     Find match.  The editor looks forward for the nearest parenthesis, bracket, or brace
	     and then moves the cursor to the matching parenthesis, bracket, or brace.

     [n]fc   Move forward to the nth occurrence of the character c.

     [n]Fc   Move backward to the nth occurrence of the character c.

     [n]tc   Move forward to just before the nth occurrence of the character c.

     [n]Tc   Move backward to just before the nth occurrence of the character c.

     [n];    Repeats the last f, F, t, or T command.

     [n],    Repeats the last f, F, t, or T command, but moves in the opposite direction.

     Inter-line movement commands:

     [n]j, [n]+, and [n]^N
	     Move to the nth next line in the history.

     [n]k, [n]-, and [n]^P
	     Move to the nth previous line in the history.

     [n]G    Move to line n in the history; if n is not specified, the number of the first remem-
	     bered line is used.

     [n]g    Like G, except if n is not specified, it goes to the most recent remembered line.

	     Search backward through the history for the nth line containing string; if string
	     starts with '^', the remainder of the string must appear at the start of the history
	     line for it to match.

	     Same as /, except it searches forward through the history.

     [n]n    Search for the nth occurrence of the last search string; the direction of the search
	     is the same as the last search.

     [n]N    Search for the nth occurrence of the last search string; the direction of the search
	     is the opposite of the last search.

	     Take the characters from the beginning of the line to the current cursor position as
	     search string and do a backwards history search for lines beginning with this
	     string; keep the cursor position.	This works only in insert mode and keeps it

     Edit commands

     [n]a    Append text n times; goes into insert mode just after the current position.  The
	     append is only replicated if command mode is re-entered i.e. <esc> is used.

     [n]A    Same as a, except it appends at the end of the line.

     [n]i    Insert text n times; goes into insert mode at the current position.  The insertion
	     is only replicated if command mode is re-entered i.e. <esc> is used.

     [n]I    Same as i, except the insertion is done just before the first non-blank character.

     [n]s    Substitute the next n characters (i.e. delete the characters and go into insert

     S	     Substitute whole line.  All characters from the first non-blank character to the end
	     of the line are deleted and insert mode is entered.

	     Change from the current position to the position resulting from n move-cmds (i.e.
	     delete the indicated region and go into insert mode); if move-cmd is c, the line
	     starting from the first non-blank character is changed.

     C	     Change from the current position to the end of the line (i.e. delete to the end of
	     the line and go into insert mode).

     [n]x    Delete the next n characters.

     [n]X    Delete the previous n characters.

     D	     Delete to the end of the line.

	     Delete from the current position to the position resulting from n move-cmds;
	     move-cmd is a movement command (see above) or d, in which case the current line is

     [n]rc   Replace the next n characters with the character c.

     [n]R    Replace.  Enter insert mode but overwrite existing characters instead of inserting
	     before existing characters.  The replacement is repeated n times.

     [n]~    Change the case of the next n characters.

	     Yank from the current position to the position resulting from n move-cmds into the
	     yank buffer; if move-cmd is y, the whole line is yanked.

     Y	     Yank from the current position to the end of the line.

     [n]p    Paste the contents of the yank buffer just after the current position, n times.

     [n]P    Same as p, except the buffer is pasted at the current position.

     Miscellaneous vi commands

     ^J and ^M
	     The current line is read, parsed, and executed by the shell.

     ^L and ^R
	     Redraw the current line.

     [n].    Redo the last edit command n times.

     u	     Undo the last edit command.

     U	     Undo all changes that have been made to the current line.

     intr and quit
	     The interrupt and quit terminal characters cause the current line to be deleted and
	     a new prompt to be printed.

     ~/.mkshrc		User mkshrc profile (non-privileged interactive shells); see Startup
			files. The location can be changed at compile time (for embedded sys-
			tems); AOSP Android builds use /system/etc/mkshrc.
     ~/.profile 	User profile (non-privileged login shells); see Startup files near the
			top of this manual.
     /etc/profile	System profile (login shells); see Startup files.
     /etc/shells	Shell database.
     /etc/suid_profile	Suid profile (privileged shells); see Startup files.

     Note: On Android, /system/etc/ contains the system and suid profile.

     awk(1), cat(1), ed(1), getopt(1), sed(1), sh(1), stty(1), dup(2), execve(2), getgid(2),
     getuid(2), mknod(2), mkfifo(2), open(2), pipe(2), rename(2), wait(2), getopt(3),
     nl_langinfo(3), setlocale(3), signal(3), system(3), tty(4), shells(5), environ(7),
     script(7), utf-8(7), mknod(8)



     Morris Bolsky, The KornShell Command and Programming Language, Prentice Hall PTR, xvi + 356
     pages, 1989, ISBN 978-0-13-516972-8 (0-13-516972-0).

     Morris I. Bolsky and David G. Korn, The New KornShell Command and Programming Language (2nd
     Edition), Prentice Hall PTR, xvi + 400 pages, 1995, ISBN 978-0-13-182700-4 (0-13-182700-6).

     Stephen G. Kochan and Patrick H. Wood, UNIX Shell Programming, Hayden, Revised Edition,
     xi + 490 pages, 1990, ISBN 978-0-672-48448-3 (0-672-48448-X).

     IEEE Inc., IEEE Standard for Information Technology - Portable Operating System Interface
     (POSIX), IEEE Press, Part 2: Shell and Utilities, xvii + 1195 pages, 1993, ISBN
     978-1-55937-255-8 (1-55937-255-9).

     Bill Rosenblatt, Learning the Korn Shell, O'Reilly, 360 pages, 1993, ISBN 978-1-56592-054-5

     Bill Rosenblatt and Arnold Robbins, Learning the Korn Shell, Second Edition, O'Reilly, 432
     pages, 2002, ISBN 978-0-596-00195-7 (0-596-00195-9).

     Barry Rosenberg, KornShell Programming Tutorial, Addison-Wesley Professional, xxi + 324
     pages, 1991, ISBN 978-0-201-56324-5 (0-201-56324-X).

     The MirBSD Korn Shell is developed by Thorsten Glaser <tg@mirbsd.org> and currently main-
     tained as part of The MirOS Project.  This shell is based upon the Public Domain Korn SHell.
     The developer of mksh recognises the efforts of the pdksh authors, who had dedicated their
     work into Public Domain, our users, and all contributors, such as the Debian and OpenBSD
     projects.	See the documentation, CVS, and web site for details.

     mksh only supports the Unicode BMP (Basic Multilingual Plane).

     mksh has a different scope model from AT&T UNIX ksh, which leads to subtile differences in
     semantics for identical builtins.	This can cause issues with a nameref to suddenly point to
     a local variable by accident; fixing this is hard.

     The parts of a pipeline, like below, are executed in subshells.  Thus, variable assignments
     inside them fail.	Use co-processes instead.

	   foo | bar | read baz 	   # will not change $baz
	   foo | bar |& read -p baz	   # will, however, do so

     mksh provides a consistent set of 32-bit integer arithmetics, both signed and unsigned, with
     defined wraparound and sign of the result of a modulo operation, even (defying POSIX) on
     64-bit systems.  If you require 64-bit integer arithmetics, use lksh (legacy mksh) instead,
     but be aware that, in POSIX, it's legal for the OS to make print $((2147483647 + 1)) delete
     all files on your system, as it's Undefined Behaviour.

     Suspending (using ^Z) pipelines like the one below will only suspend the currently running
     part of the pipeline; in this example, ``fubar'' is immediately printed on suspension (but
     not later after an fg).

	   $ /bin/sleep 666 && echo fubar

     This document attempts to describe mksh R46 and up, compiled without any options impacting
     functionality, such as MKSH_SMALL, when not called as /bin/sh which, on some systems only,
     enables set -o sh automatically (whose behaviour differs across targets), for an operating
     environment supporting all of its advanced needs.	Please report bugs in mksh to the MirOS
     mailing list at <miros-mksh@mirbsd.org> or in the #!/bin/mksh (or #ksh) IRC channel at
     irc.freenode.net (Port 6697 SSL, 6667 unencrypted), or at: https://launchpad.net/mksh

MirBSD					   May 2, 2013					   MirBSD

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