MKSH(1) BSD General Commands Manual MKSH(1)
NAME
mksh, sh -- MirBSD Korn shell
SYNOPSIS
mksh [-+abCefhiklmnprUuvXx] [-T /dev/ttyCn | -] [-+o option] [-c string | -s | file [argument ...]]
builtin-name [argument ...]
DESCRIPTION
mksh is a command interpreter intended for both interactive and shell script use. Its command language is a superset of the sh(C) shell lan-
guage and largely compatible to the original Korn shell.
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 effec-
tive 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 following restrictions come into effect after the shell
processes any profile and ENV files:
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 positional 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 executed, or
zero, if no command is executed.
Startup files
For the actual location of these files, see FILES. A login shell processes the system profile 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 ignored.
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 beginning 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 command words,
if any, define the command that is to be executed and its arguments. The command 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 con-
structs 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 sta-
tus of a command consisting only of parameter assignments is that of the last command substitution performed 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 standard 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. 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 commands 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, redirections 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 semi-
colon, a newline, or a (syntactically correct) 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 }
(list)
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 associated 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 restrictions 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 executed, 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 statement is the last exit status of list; if list is never
executed, the exit status is zero.
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 enu-
merated 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 reasons, 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 zero.
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 exceptions:
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 comparison [[ foobar = f*r ]] succeeds). This even works
indirectly:
$ bar=foobar; baz='f*r'
$ [[ $bar = $baz ]]; echo $?
$ [[ $bar = "$baz" ]]; echo $?
Perhaps surprisingly, the first comparison succeeds, whereas the second doesn't.
Quoting
Quoting is used to prevent the shell from treating characters or words specially. There are three methods of quoting. First, '' quotes the
following character, unless it is at the end of a line, in which case both the '' and the newline are stripped. Second, a single quote
(''') quotes everything up to the next single quote (this may span lines). Third, a double quote ('"') quotes all characters, except '$',
'`' 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 following 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', '',
'f', '
', '
', ' ', '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 charac-
ter.
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 (' ###'); 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; hexadecimal 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 newline.
Aliases
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 command aliases (i.e. substitutes the alias name for its value) when it reads the first word of a com-
mand. 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 specifically 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'
local='typeset'
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 automatically for non-interactive shells. For interactive shells, only the fol-
lowing 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).
Substitution
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 (deprecated) `command`; and arithmetic substitutions take the form
$((expression)).
If a substitution appears outside of double quotes, the results of the substitution are generally subject to word or field splitting accord-
ing to the current value of the IFS parameter. 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 combination with zero or one non-IFS whitespace octets, delimit a field. As a special case, leading and trailing
IFS whitespace and trailing IFS non-whitespace are stripped (i.e. no leading 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 substitution. 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 incompati-
ble 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 sec-
tions below).
A command substitution is replaced by the output generated by the specified command which is run in a subshell. For $(command) substitu-
tions, 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
EOF
Arithmetic substitutions are replaced by the value of the specified expression. For example, the command print $((2+3*4)) displays 14. See
Arithmetic expressions for a description of an expression.
Parameters
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 punctuation or digit character parameters described below, or a letter followed by zero or more let-
ters 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 parameter (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 single 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 param-
eter 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 com-
mands; see their descriptions 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 automat-
ically sets the export attribute for those parameters.
Modifiers can be applied to the ${name} form of parameter substitution:
${name:-word}
If name is set and not NULL, it is substituted; otherwise, word is substituted.
${name:+word}
If name is set and not NULL, word is substituted; otherwise, nothing is substituted.
${name:=word}
If name is set and not NULL, it is substituted; otherwise, it is assigned word and the resulting value of name is substituted.
${name:?word}
If name is set and not NULL, it is substituted; otherwise, word is printed on standard 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 printed.
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 evaluated.
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):
${#name}
The number of positional parameters if name is '*', '@', or not specified; otherwise the length (in characters) of the string value
of parameter name.
${#name[*]}
${#name[@]}
The number of elements in the array name.
${%name}
The width (in screen columns) of the string value of parameter name, or -1 if ${name} contains a control character.
${!name}
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).
${!name[*]}
${!name[@]}
The names of indices (keys) in the array name.
${name#pattern}
${name##pattern}
If pattern matches the beginning of the value of parameter name, the matched text is deleted from the result of substitution. A sin-
gle '#' 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[@]}).
${name%pattern}
${name%%pattern}
Like ${..#..} substitution, but it deletes from the end of the value. Cannot be applied to a vector.
${name/pattern/string}
${name//pattern/string}
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. 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.
${name:pos:len}
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, opening 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.
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 argu-
ments 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 command. In interactive use, this parameter is also set in the parent shell to the last word of the
previous command.
CDPATH Search path for the cd built-in command. It works the same way as PATH for those directories not beginning with '/' in cd com-
mands. Note that if CDPATH is set and does not contain '.' or contains an empty path, the current directory 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; similar for LINES. This parameter is used by the interactive line editing modes, and by the select,
set -o, and kill -l commands to format information columns.
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 500.
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 started.
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 sec-
tions, below.
LINENO The line number of the function or shell script that is currently being executed.
LINES Set to the number of lines on the terminal or window. Always set, defaults to 24.
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 commands 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 number (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 '#' charac-
ter, 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:=$(hostname)} and the root-vs-user distinguishing clause are (in this example) executed 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 latter is more practical. This is a more complex example, avoiding to directly enter special charac-
ters (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 pressure from David G. Korn, mksh now also supports the following form:
PS1=$'1
1e[7m1$PWD1e[0m1> '
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 performed before it is printed. The default is '+ '.
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 fol-
lowing 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:
prefix{str1,...,strN}suffix
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 expan-
sion 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 meaning:
? 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.
*(pattern|...|pattern)
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.
+(pattern|...|pattern)
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.
?(pattern|...|pattern)
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''.
@(pattern|...|pattern)
Matches a string that matches one of the specified patterns. Example: The pattern @(foo|bar) only matches the strings ``foo'' and
``bar''.
!(pattern|...|pattern)
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 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 exceptions 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 temporary file until a line matching marker is read. When the command is executed, standard input is redi-
rected 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, command, and arithmetic substitutions are performed,
along with backslash ('') escapes for '$', '`', '', and '
ewline', 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 substitu-
tion 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 string.
<& fd Standard input is duplicated from file descriptor fd. fd can be a number, indicating 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 '-', indi-
cating standard input is to be closed. Note that fd is limited 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.
&>| file, &>> file, &>& fd
Same as >| file, >> file, or >& fd, followed by 2>&1, as above. These are mksh extensions.
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 substitu-
tions, 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 '#' char-
acter, 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 increasing 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 specified 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. It is discouraged to
prefix numbers with a sole zero ('0'), because some shells may interpret them as base-8 integers. 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 set-
ting). 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 -
Negation.
! 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 side.
= 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 argu-
ment 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 argu-
ment 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 not.
<= >= >
Less than or equal, greater than or equal, greater than. See <.
<< >> Shift left (right); the result is the left argument with its bits shifted left (right) by the amount given in the right argu-
ment.
+ - * /
Addition, subtraction, multiplication, and division.
% Remainder; the result is the remainder of the division of the left argument by the right. The sign of the result is unspeci-
fied if either argument is negative.
<arg1>?<arg2>:<arg3>
If <arg1> is non-zero, the result is <arg2>; otherwise the result is <arg3>.
Co-processes
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 portion 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
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 commands, before regular and
non-regular built-ins, and before 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 def-
initions 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 exe-
cuted; 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), 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 function 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 untouched).
o Parameter assignments preceding function calls are not kept in the shell environment (executing Bourne-style functions will keep assign-
ments).
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 func-
tion (Bourne-style functions leave OPTIND untouched, so using getopts inside a function interferes with using getopts outside the func-
tion).
o Bourne-style function definitions take precedence over alias dereferences and remove alias definitions upon encounter, while aliases take
precedence over Korn-style functions.
In the future, the following differences will 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 func-
tion.
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, a
function, a regular built-in, or the name of a file to execute found using the PATH parameter. The checks are made in the above order. Spe-
cial built-in commands differ from other commands in that the PATH parameter 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 regular:
POSIX special commands
., :, break, continue, eval, exec, exit, export, readonly, return, set, shift, trap, unset, wait
Additional mksh special commands
builtin, global, times, typeset
Very special commands (non-POSIX)
alias, readonly, set, typeset
POSIX regular commands
alias, bg, cd, command, false, fc, fg, getopts, jobs, kill, read, true, umask, unalias
Additional mksh regular commands
[, chdir, bind, cat, echo, let, mknod, print, printf, pwd, realpath, rename, sleep, test, ulimit, whence
In the future, the additional mksh special and regular commands may be treated differently from the POSIX special and regular commands.
Once the type of command has been determined, any command-line parameter assignments are performed and exported for the duration of the com-
mand.
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 direc-
tories of PATH. If arguments are given, the positional parameters may be used to access them while file is being executed. If no
arguments are given, the positional parameters are those of the environment the command is used in.
: [...]
The null command. Exit status is set to zero.
alias [-d | -t [-r] | +-x] [-p] [+] [name [=value] ...]
Without arguments, alias lists all aliases. For any name without a value, the existing 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 effect).
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 information.
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 optionally succeded by a tilde character. Future input of the string will cause the editing 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 (usu-
ally 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 ter-
minal 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 compiled 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 directory. 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 parameters are updated to reflect the current and old working direc-
tory, 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 permanent).
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 or the much slower POSIX utility printf 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 recog-
nised.
The options are provided for compatibility with BSD shell scripts. The -n option suppresses the trailing newline, -e enables back-
slash 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 interpretation 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 cur-
rent 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 descrip-
tors greater than 2 which are opened or dup(2)'d in this way are not made available to other executed commands (i.e. commands 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 specified, 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 specified, 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 character 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 pre-
fixed 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 ille-
gal 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 status. 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 whenever 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 results.
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 command.
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".
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 (character type device), or p (named pipe, FIFO). The
file created may be modified according 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 utility printf, except that it uses the same Backslash expansion and I/O code as the
rest of mksh. This is not normally part of mksh; however, distributors may have added this as builtin as a speed hack.
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 following '..' 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 parameters 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 occurs.
-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 charac-
ter.
-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 processed.
-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 for:
find . -type f -print0 |
while IFS= read -d '' -r filename; do
print -r -- "found <${filename#./}>"
done
The inner loop will be executed in a subshell and variable changes cannot be propagated 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, parameters 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 printed.
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; otherwise, 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 situa-
tions 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 . scripts.
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 ! state-
ments.
-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 aforementioned 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 '=' modi-
fiers 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 commands and parameter assignments 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 trans-
pose-chars (^T) acts slightly differently.
-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. Currently 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 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 autode-
tection 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 options.
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 -L.
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 opera-
tors (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 arguments to test or inside the brackets [ ... ] is less
than five: if leading '!' arguments can be stripped such that only one to three arguments remain, then the lowered comparison is exe-
cuted; (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-argument 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" ]]''
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 running 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 do.
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, indicat-
ing 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 above).
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 cannot 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 functions 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 parameters, 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 parameters.
-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). Parameters with this attribute may be assigned values containing arithmetic expressions.
-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 specified, 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 on.
-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 process.
-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) used.
-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 number.
Symbolic masks are like those used by chmod(1). When used, they describe what permissions 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 finish and exits with a zero status. If job monitor-
ing is enabled, the completion status 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, function, tracked alias, or executable). If the -p
option is used, a path search is performed 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 background 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 commands, and non-built-in, non-function commands) can be
stopped; commands like read cannot be.
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
where...
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 necessarily 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 indicates 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 session, 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 command. 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 parameter), 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 interrupted.
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 alphanumerics, underscore ('_'), and dollar sign ('$') char-
acters.
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); otherwise, 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 completions 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 buf-
fer, so down-history is not useful 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 command 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 terminal 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 performing 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; otherwise 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 partial word containing the cursor. File type indica-
tors 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 line.
search-character-backward: [n] ^[^]
Search backward in the current line for the nth occurrence of the next character typed.
search-character-forward: [n] ^]
Search forward in the current line for the nth occurrence of the next character typed.
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 previous characters; otherwise, it exchanges the previ-
ous 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, optionally, <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 (:) com-
mands).
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 mode:
^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 vi-tabcomplete.
In command mode, each character is interpreted as a command. Characters that don't correspond to commands, are illegal combinations of com-
mands, or are commands that can't be carried out, all cause beeps. In the following command descriptions, an [n] indicates the command 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 line.
[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 com-
mand/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 paren-
thesis, 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 remembered line is used.
[n]g Like G, except if n is not specified, it goes to the most recent remembered line.
[n]/string
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.
[n]?string
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.
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 mode).
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.
[n]cmove-cmd
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.
[n]dmove-cmd
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 deleted.
[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.
[n]ymove-cmd
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.
FILES
~/.mkshrc User mkshrc profile (non-privileged interactive shells); see Startup files. The location can be changed at compile time
(for embedded systems); 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.
SEE ALSO
awk(1), cat(1), ed(1), getopt(1), printf(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)
http://docsrv.sco.com:507/en/man/html.C/sh.C.html
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 (1-56592-054-6).
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).
AUTHORS
The MirBSD Korn Shell is developed by Thorsten Glaser <tg@mirbsd.org> and currently maintained 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.
CAVEATS
mksh only supports the Unicode BMP (Basic Multilingual Plane). It has a different scope model from AT&T UNIX ksh, which leads to subtile
differences in semantics for identical builtins.
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
BUGS
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 R40+CVS and up, compiled without any options impacting functionality, such as MKSH_SMALL, for an
operating environment supporting all of its advanced needs. Please report bugs in mksh to the MirOS mailing list at
<miros-discuss@mirbsd.org> or in the #!/bin/mksh (or #ksh) IRC channel at irc.freenode.net (Port 6697 SSL, 6667 unencrypted).
MirBSD June 29, 2012 MirBSD
