Visit The New, Modern Unix Linux Community

Linux and UNIX Man Pages

Test Your Knowledge in Computers #980
Difficulty: Easy
Releases of Mac OS X from 1999 to 2005 ran on the Intel-based Macs of that period.
True or False?
Linux & Unix Commands - Search Man Pages

csh(1) [hpux man page]

csh(1)							      General Commands Manual							    csh(1)

NAME
csh - a shell (command interpreter) with C-like syntax SYNOPSIS
[command_file] [argument_list ...] DESCRIPTION
is a command language interpreter that incorporates a command history buffer, C-like syntax, and job control facilities. Command Options Command options are interpreted as follows: Read commands from the (single) following argument which must be present. Any remaining arguments are placed in C shell exits if any invoked command terminates abnormally or yields a non-zero exit status. Suppress execution of the file in your home directory, thus speeding up shell start-up time. Force to respond interactively when called from a device other than a computer terminal (such as another computer). normally responds non-interactively. If is called from a computer terminal, it always responds interactively, regardless of which options are selected. Parse but do execute commands. This is useful for checking syntax in shell scripts. All substitutions are performed (history, com- mand, alias, etc.). Take command input from the standard input. Read and execute a single line of input. Set the shell variable, causing command input to be echoed to the standard output device after history substitutions are made. Set the shell variable, causing all commands to be echoed to the standard error immediately before execution. Disable the tenex features which use the ESC key for command/file name completion and CTRL-D for listing available files (see the section below) Set the variable before is executed so that all commands are also echoed to the standard output. Set the variable before is executed so that all commands are also echoed to the standard output. After processing the command options, if arguments remain in the argument list, and the or options were not specified, the first remaining argument is taken as the name of a file of commands to be executed. COMMANDS A simple command is a sequence of words, the first of which specifies the command to be executed. A sequence of simple commands separated by vertical bar characters forms a pipeline. The output of each command in a pipeline becomes the input for the next command in the pipe- line. Sequences of pipelines can be separated by semicolons which causes them to be executed sequentially. A sequence of pipelines can be executed in background mode by adding an ampersand character after the last entry. Any pipeline can be placed in parentheses to form a simple command which, in turn, can be a component of another pipeline. Pipelines can also be separated by or indicating, as in the C language, that the second pipeline is to be executed only if the first fails or succeeds, respectively. Jobs associates a with each pipeline and keeps a table of current jobs (printed by the command) and assigns them small integer numbers. When a job is started asynchronously using the shell prints a line resembling: [1] 1234 indicating that the job which was started asynchronously was job number 1 and had one (top-level) process, whose process id was 1234. If you are running a job and want to do something else, you can type the currently defined suspend character (see termio(7)) which sends a stop signal to the current job. then normally indicates that the job has been `Stopped', and prints another prompt. You can then manipu- late the state of this job, putting it in the background with the command, run some other commands, and then eventually bring the job back into the foreground with the foreground command A suspend takes effect immediately and is like an interrupt in that pending output and unread input are discarded when it is typed. There is a delayed suspend character which does not generate a stop signal until a program attempts to read(2) it. This can usefully be typed ahead when you have prepared some commands for a job which you want to stop after it has read them. A job being run in the background stops if it tries to read from the terminal. Background jobs are normally allowed to produce output, but this can be disabled by giving the command (see stty(1)). If you set this tty option, background jobs stop when they try to produce out- put, just as they do when they try to read input. Keyboard signals and line-hangup signals from the terminal interface are not sent to background jobs on such systems. This means that background jobs are immune to the effects of logging out or typing the interrupt, quit, suspend, and delayed suspend characters (see termio(7)). There are several ways to refer to jobs in the shell. The character introduces a job name. If you wish to refer to job number 1, you can name it as Just naming a job brings it to the foreground; thus is a synonym for bringing job 1 back into the foreground. Similarly, typing resumes job 1 in the background. Jobs can also be named by prefixes of the string typed in to start them if these prefixes are unambigu- ous; thus normally restarts a suspended ex(1) job, if there is only one suspended job whose name begins with the string It is also possible to say which specifies a job whose text contains string, if there is only one such job. maintains a notion of the current and previous jobs. In output pertaining to jobs, the current job is marked with a and the previous job with a The abbreviation refers to the current job and refers to the previous job. For close analogy with the syntax of the mechanism (described below), is also a synonym for the current job. learns immediately whenever a process changes state. It normally informs you whenever a job becomes blocked so that no further progress is possible, but only just before printing a prompt. This is done so that it does not otherwise disturb your work. If, however, you set the shell variable notifies you immediately of changes in status of background jobs. There is also a built-in command called which marks a single process so that any status change is immediately reported. By default, marks the current process. Simply type after starting a background job to mark it. If you try to leave the shell while jobs are stopped, sends the warning message: Use the command to see what they are. If you do this or immediately try to exit again, does not warn you a second time, and the suspended jobs are terminated (see exit(2)). Built-In Commands Built-in commands are executed within the shell without spawning a new process. If a built-in command occurs as any component of a pipe- line except the last, it is executed in a subshell. The built-in commands are: The first form prints all aliases. The second form prints the alias for name. The third form assigns the specified wordlist as the alias of name. Command and file name substitution are performed on wordlist. name cannot be or Put the current (job not specified) or specified jobs into the background, continuing them if they were stopped. Causes execution to resume after the of the nearest enclosing or The remaining commands on the current line are executed. Multi-level breaks are thus possible by writing them all on one line. Causes a break from a resuming after the A label in a statement as discussed below. Change the shell's current working directory to directory_name. If not specified, directory_name defaults to your home directory. If directory_name is not found as a subdirectory of the current working directory (and does not begin with or each component of the variable cdpath is checked to see if it has a subdirectory directory_name. Finally, if all else fails, treats direc- tory_name as a shell variable. If its value begins with this is tried to see if it is a directory. See also cd(1). Continue execution of the nearest enclosing or The rest of the commands on the current line are executed. Labels the default case in a statement. The default should come after all other labels. Prints the directory stack; the top of the stack is at the left; the first directory in the stack is the current directory. The specified words are written to the shell's standard output, separated by spaces, and terminated with a new-line unless the option is specified. See also echo(1). See the descriptions of the and statements below. (Same behavior as sh(1).) arguments are read as input to the shell and the resulting command(s) executed. This is usually used to execute commands generated as the result of command or variable substitution, since parsing occurs before these substitutions. The specified command is executed in place of the current shell. exits either with the value of the variable (first form) or with the value of the specified expression (second form). Brings the current (job not specified) or specified jobs into the foreground, continuing them if they were stopped. The variable name is successively set to each member of wordlist and the sequence of commands between this command and the matching are executed. (Both and must appear alone on separate lines.) The built-in command can be used to continue the loop prematurely; the built-in command to terminate it prematurely. When this command is read from the terminal, the loop is read once, prompting with before any statements in the loop are exe- cuted. If you make a mistake while typing in a loop at the terminal, use the erase or line-kill character as appropriate to recover. Like but no escapes are recognized and words are delimited by null characters in the output. Useful in programs that use the shell to perform file name expansion on a list of words. The specified word is file name and command expanded to yield a string of the form The shell rewinds its input as much as possible and searches for a line of the form possibly preceded by blanks or tabs. Execution continues after the specified line. Print a statistics line indicating how effective the internal hash table has been at locating commands (and avoiding An is attempted for each component of the path where the hash function indicates a possible hit, and in each component that does not begin with a Displays the history event list. If n is given, only the n most recent events are printed. The option reverses the order of printout to be most recent first rather than oldest first. The option prints the history list without leading numbers for producing files suitable for the command. If expression evaluates true, the single command with arguments is executed. Variable substitution on command happens early, at the same time it does for the rest of the command. command must be a simple command; not a pipeline, a command list, a parenthesized command list, or an aliased command. Input/output redirection occurs even if expression is false, meaning that command is executed (this is a bug). If expression1 is true, all commands down to the first are executed; otherwise if expression2 is true, all commands from the first down to the second are executed, etc. Any number of pairs are possible, but only one is needed. The part is likewise optional. (The words and must appear at the beginning of input lines. The must appear alone on its input line or after an Lists active jobs. The option lists process IDs in addition to the usual information. Sends either the TERM (terminate) signal or the specified signal to the specified jobs or processes. Signals are either given by number or by names (as given in stripped of the prefix (see signal(2)). The signal names are listed by There is no default, so used alone does not send a signal to the current job. If the signal being sent is TERM (terminate) or HUP (hangup), the job or process is sent a CONT (continue) signal as well. See also kill(1). Limits the usage by the current process and each process it creates not to (individually) exceed maximum_use on the specified resource. If maximum_use is not specified, then the current limit is displayed; if resource is not specified, then all limitations are given. If the flag is specified, the hard limits are used instead of the current limits. The hard limits impose a ceiling on the values of the current limits. Only the superuser can raise the hard limits, but a user can lower or raise the current lim- its within the legal range. Controllable resources currently include: Maximum address space in bytes for a process Size of the largest core dump that is created Maximum number of CPU seconds to be used by each process Maximum growth of the data region allowed beyond the end of the program text Maximum number of open files for each process Largest single file that can be created Maximum size to which a process's resident set size can grow Maximum size of the automatically extended stack region The maximum_use argument can be specified as a floating-point or integer number followed by a scale factor: k or kilobytes (1024 bytes), m or megabytes, or b or blocks (the units used by the ulimit system call). For both resource names and scale factors, unambiguous prefixes of the names can be used. filesize can be lowered by an instance of but can only be raised by an instance whose effective user ID is root. For more information, refer to the documentation for the ulimit system call. Terminates a login shell, replacing it with an instance of This is one way to log off, included for compatibility with sh(1). Terminates a login shell. Especially useful if ignoreeof is set. A similar function, which works for sessions that are not login shells, is provided for historical reasons. Its use is not recommended because it is not part of the standard BSD and may not be supported in future releases. Changes the group identification of the caller; for details see newgrp(1). A new shell is executed by so that the current shell environment is lost. The first form sets the nice (run command priority) for this shell to 4 (the default). The second form sets the priority to the given number. The final two forms run command at priority 4 and number respectively. The user with appropriate privileges can raise the pri- ority by specifying negative niceness using command is always executed in a sub-shell, and restrictions placed on commands in simple statements apply. See also nice(1). Without an argument, can be used in shell scripts to cause hangups to be ignored for the remainder of the script. With an argument, causes the specified command to be run with hangups ignored. All processes executed in the background with are effectively as described under Jobs in the section. Causes the shell to notify the user asynchronously when the status of the current (job not specified) or specified jobs changes; normally notification is presented before a prompt. This is auto- matic if the shell variable notify is set. Controls the action of the shell on interrupts. With no arguments, onintr restores the default action of the shell on interrupts, which action is to terminate shell scripts or return to the terminal command input level. If is specified, all interrupts are ignored. If a label is given, the shell executes a when an interrupt is received or a child process terminates because it was interrupted. If the shell is running in the background and interrupts are being ignored, onintr has no effect; interrupts continue to be ignored by the shell and all invoked commands. Pops the directory stack, returning to the new top directory. With an argument, discards the nth entry in the stack. The elements of the directory stack are numbered from 0 starting at the top. A synonym for called is provided for historical reasons. Its use is not recommended because it is not part of the standard BSD and may not be supported in future releases. With no arguments, pushd exchanges the top two elements of the directory stack. Given a name argument, pushd changes to the new directory (using cd) and pushes the old current working directory (as in csw) onto the directory stack. With a numeric argument, pushd rotates the nth argument of the directory stack around to be the top element and changes to that directory. The mem- bers of the directory stack are numbered from the top starting at 0. A synonym for pushd, called gd, is provided for his- torical reasons. Its use is not recommended since it is not part of the standard BSD and may not be supported in future releases. Causes the internal hash table of the contents of the directories in the path variable to be recomputed. This is needed if new commands are added to directories in the path while you are logged in. This should only be necessary if you add commands to one of your own directories or if a systems programmer changes the contents of one of the system directories. The specified command (which is subject to the same restrictions as the command in the one-line statement above) is executed count times. I/O redirections occur exactly once, even if count is 0. The first form of shows the value of all shell variables. Variables whose value is other than a single word print as a parenthesized word list. The second form sets name to the null string. The third form sets name to the single word. The fourth form sets the indexth component of name to word; this component must already exist. The final form sets name to the list of words in wordlist. In all cases the value is command and file-name expanded. These arguments can be repeated to set multiple values in a single set command. Note, however, that variable expansion hap- pens for all arguments before any setting occurs. Sets the value of environment variable name to be value, a single string. The most commonly used environment variables, and are automatically imported to and exported from the variables user, term, and path; there is no need to use for these. If no argument is given, the members of are shifted to the left, discarding An error occurs if is not set or has less than two strings assigned to it. When vari- able is specified, shift performs the same function on the specified variable. reads commands from name. commands can be nested, but if nested too deeply the shell may run out of file descriptors or reach the max stack size (see maxssiz(5)). An error in a at any level terminates all nested commands. Normally, input during commands is not placed on the history list. The option can be used to place commands in the history list without being executing them. Stops the current (no argument) or specified jobs executing in the background. Causes to stop as if it had been sent a suspend signal. Since normally ignores suspend signals, this is the only way to suspend the shell. This command gives an error message if attempted from a login shell. Each label (str1) is successively matched against the specified string which is first command and file name expanded. The form of the labels is the Pattern Matching Notation with the exception that non-matching lists in bracket expressions are not supported (see regexp(5)). If none of the labels match before a label is found, the execution begins after the label. Each label and the label must appear at the beginning of a line. The command causes execution to continue after the endsw. Oth- erwise, control may fall through labels and labels as in C. If no label matches and there is no default, execution contin- ues after the When command is not specified, a summary of time used by this shell and its children is printed. If specified, the simple com- mand is timed and a time summary as described under the variable is printed. If necessary, an extra shell is created to print the time statistic when the command completes. The current file creation mask is displayed (value not specified) or set to the specified value. The mask is given in octal. Common values for the mask are which gives all permissions to the owner and group and read and execute permissions to all others, or which gives all permissions to the owner, and only read and execute permission to the group and all others. See also umask(1). All aliases whose names match the specified pattern are discarded. Thus, all aliases are removed by No error occurs if pattern does not match an existing alias. Use of the internal hash table to speed location of executed programs is disabled. All variables whose names match the specified pattern are removed. Thus, all variables are removed by this has noticeably undesirable side-effects. No error occurs if pattern matches nothing. Removes all variables whose names match the specified pattern from the environment. See also the command above and printenv(1). Waits for all background jobs to terminate. If the shell is interactive, an interrupt can disrupt the wait, at which time the shell prints names and job numbers of all jobs known to be outstanding. While the specified expression evaluates non-zero, the commands between the and the matching are evaluated. and can be used to terminate or continue the loop prematurely. (The and must appear alone on their input lines.) If the input is a terminal (i.e., not a script), prompting occurs the first time through the loop as for the statement. Brings the specified job into the foreground. Continues the specified job in the background. The first form prints the values of all the shell variables. The second form sets the specified name to the value of expression. If the expression contains or at least this part of the expression must be placed within parentheses. The third form assigns the value of expression to the indexth argument of name. Both name and its indexth component must already exist. The operators etc., are available as in C. White space can optionally separate the name from the assignment operator. How- ever, spaces are mandatory in separating components of expression which would otherwise be single words. Special postfix and operators increment and decrement name, respectively (e.g., Non-Built-In Command Execution When a command to be executed is not a built-in command, attempts to execute the command via exec(2). Each word in the variable path names a directory in which the shell attempts to find the command (if the command does not begin with If neither nor is given, the shell hashes the names in these directories into an internal table so that an exec is attempted only in those directories where the command might possi- bly reside. This greatly speeds command location when a large number of directories are present in the search path. If this mechanism has been turned off (via or if or was given, or if any directory component of path does not begin with a the shell concatenates the directory name and the given command name to form a path name of a file which it then attempts to execute. Commands placed inside parentheses are always executed in a subshell. Thus prints the home directory then returns to the current directory upon completion, whereas: remains in the home directory upon completion. When commands are placed inside parentheses, it is usually to prevent chdir from affecting the current shell. If the file has execute permissions but is not an executable binary file, it is assumed to be a script file, which is a file of data for an interpreter that is executed as a separate process. first attempts to load and execute the script file (see exec(2)). If the first two characters of the script file are exec(2) expects an interpreter path name to follow and attempts to execute the specified interpreter as a separate process to read the entire script file. If no is named, and there is an alias for the shell, the words of the alias are inserted at the beginning of the argument list to form the shell command. The first word of the alias should be the full path name of the command to be used. Note that this is a special, late- occurring case of alias substitution, which inserts words into the argument list without modification. If no is named and there is no shell alias, but the first character of the file is the interpreter named by the variable is executed (note that this normally would be unless the user has reset If is not set, is executed. If no is named, and there is no shell alias, and the first character of the file is not is executed to interpret the script file. History Substitutions History substitutions enable you to repeat commands, use words from previous commands as portions of new commands, repeat arguments of a previous command in the current command, and fix spelling or typing mistakes in an earlier command. History substitutions begin with an exclamation point Substitutions can begin anywhere in the input stream, but cannot be nested. The exclamation point can be preceded by a backslash to cancel its special meaning. For convenience, an exclamation point is passed to the parser unchanged when it is followed by a blank, tab, newline, equal sign, or left parenthesis. Any input line that contains history sub- stitution is echoed on the terminal before it is executed for verification. Commands input from the terminal that consist of one or more words are saved on the history list. The history substitutions reintroduce sequences of words from these saved commands into the input stream. The number of previous commands saved is controlled by the variable. The previous command is always saved, regardless of its value. Commands are numbered sequentially from 1. You can refer to previous events by event number (such as for event 10), relative event location (such as for the second previous event), full or partial command name (such as for the last event using a command with initial character and string expression (such as referring to an event containing the characters These forms, without further modification, simply reintroduce the words of the specified events, each separated by a single blank. As a special case, is a re-do; it refers to the previous command. To select words from a command, use a colon and a designator for the desired words after the event specification. The words of an input line are numbered from zero. The basic word designators are: First word (i.e., the command name itself). n nth word. First argument. (This is equivalent to Last word. Range of words from a through b. Special cases are an abbreviation for ``word 0 through word y''; and which means ``word x up to, but not includ- ing, word Range from the second word through the last word. Used with a search sequence to substitute the immediately preceding matching word. The colon separating the command specification from the word designator can be omitted if the argument selector begins with a or After word designator can be followed by a sequence of modifiers, each preceded by a colon. The following modifiers are defined: Use only the first component of a path name by removing all following components. Use the root file name by removing any trailing suffix (.xxx). Use the file name's trailing suffix by removing the root name. substitute the value of r for the value l in the indicated command. Use only the final file name of a path name by removing all leading path name components. Repeat the previous substitution. Print the new command but do not execute it. Quote the substituted words, preventing further substitutions. Like but break into words at blanks, tabs and newlines. Use a command as a prefix to another modifier to cause the specified change to be made globally. All words in the command are changed, one change per word, and each string enclosed in single quotes or double quotes is treated as a single word. Unless preceded by a the modification is applied only to the first modifiable word. An error results if a substitution is attempted and cannot be completed (i.e., if you ask for a substitution of on a history buffer containing only 10 commands). The left hand side of substitutions are strings; not regular expressions in the sense of HP-UX editors. Any character can be used as the delimiter in place of a slash Use a backslash to quote a delimiter character if it is used in the l or r string. The character in the right-hand side is replaced by the text from the left. A also quotes A null l string uses the previous string either from an l or from a contextual scan string s in The trailing delimiter in the substitution can be omitted if a new-line character follows immediately, as may the trailing in a contextual scan. A history reference can be given without an event specification (as in In this case, the reference is to the previous command unless a pre- vious history reference occurred on the same line, in which case this form repeats the previous reference. Thus gives the first and last arguments from the command matching A special abbreviation of a history reference occurs when the first non-blank character of an input line is a circumflex This is equivalent to providing a convenient shorthand for substitutions on the text of the previous line. Thus fixes the spelling of in the previous com- mand. Finally, a history substitution can be enclosed within curly braces if necessary to insulate it from the characters which follow. Thus, after one could execute to do while would look for a command starting with Quoting with Single and Double Quotes The quotation of strings by single quotes and double quotes can be used to prevent all or some of the remaining substitutions. Strings enclosed in single quotes are protected from any further interpretation. Strings enclosed in double quotes are still variable- and com- mand-expanded as described below. In both cases the resulting text becomes (all or part of) a single word. Only in one special case (see below) does a double-quoted string yield parts of more than one word; single-quoted strings never do. Alias Substitution maintains a list of aliases that can be established, displayed, and modified by the and commands. After a command line is scanned, it is parsed into distinct commands and the first word of each command, left-to-right, is checked to see if it has an alias. If it does, the text which is the alias for that command is reread with the history mechanism available as if that command was the previous input line. The resulting words replace the command and argument list. If no reference is made to the history list, the argument list is left unchanged. Thus, if the alias for is the command maps to leaving the argument list undisturbed. Similarly, if the alias for was maps to If an alias is found, the word transformation of the input text is performed and the aliasing process begins again on the re-formed input line. Looping is prevented if the first word of the new text is the same as the old by flagging it to prevent further aliasing. Other loops are detected and cause an error. Note that the mechanism allows aliases to introduce parser metasyntax. Thus: makes a command that uses pr(1) to print its arguments on the line printer. Expressions Some of the built-in commands take expressions in which the operators are similar to those of C, with the same precedence. These expres- sions appear in the and commands. The following operators are available (shown in order of increasing precedence): The following list shows the grouping of these operators. The precedence decreases from top to bottom in the list: The operators and compare their arguments as strings; all others operate on numbers. The operators and are similar to and except that the right-hand side is a pattern (containing and instances of against which the left hand operand is matched. This reduces the need for use of the statement in shell scripts when all that is really needed is pattern matching. Strings beginning with are considered octal numbers. Null or missing arguments are considered The result of all expressions are strings that represent decimal numbers. It is important to note that no two components of an expression can appear in the same word. These compo- nents should be surrounded by spaces except when adjacent to components of expressions that are syntactically significant to the parser: and Also available in expressions as primitive operands are command executions enclosed in curly braces and file enquiries of the form where l is one of: read access write access execute access existence ownership zero size plain file directory The specified filename is command- and file-name expanded then tested to see if it has the specified relationship to the real user. If the file does not exist or is inaccessible, all inquiries return false (0). Command executions succeed, returning true, if the command exits with status 0; otherwise they fail, returning false. If more detailed status information is required, the command should be executed out- side of an expression and the variable examined. Control of the Flow contains a number of commands that can be used to regulate the flow of control in command files (shell scripts) and (in limited but useful ways) from terminal input. These commands all operate by forcing the shell to reread or skip parts of its input and, due to the implemen- tation, restrict the placement of some of the commands. The and statements, as well as the form of the statement require that the major keywords appear in a single simple command on an input line as shown below. If the shell's input is not seekable, the shell buffers input whenever a loop is being read and performs seeks in this internal buffer to accomplish the rereading implied by the loop. (To the extent that this allows, backward succeed on non-seekable inputs.) Signal Handling normally ignores quit signals. Jobs running in background mode are immune to signals generated from the keyboard, including hangups. Other signals have the values which the shell inherited from its parent. handling of interrupts and terminate signals in shell scripts can be controlled by onintr. Login shells catch the terminate signal; otherwise this signal is passed on to children from the state in the shell's parent. In no case are interrupts allowed when a login shell is reading the file Command Line Parsing splits input lines into words at blanks and tabs. The following exceptions (parser metacharacters) are considered separate words: ampersand; vertical bar; semicolon; less-than sign; greater-than sign; left parenthesis; right parenthesis; double ampersand; double vertical bar; double less-than sign; double greater-than sign; comment delimiter The backslash removes the special meaning of these parser metacharacters. A parser metacharacter preceded by a backslash is interpreted as its ASCII value. A newline character (ASCII 10) preceded by a backslash is equivalent to a blank. Strings enclosed in single or double quotes form parts of a word. Metacharacters in these strings, including blanks and tabs, do not form separate words. Within pairs of backslashes or quotes, a newline preceded by a backslash gives a true newline character. When input is not a terminal, the character introduces a comment terminated by a newline. CSH VARIABLES maintains a set of variables. Each variable has a value equal to zero or more strings (words). Variables have names consisting of up to 80 letters and digits starting with a letter. The underscore character is considered a letter. The value of a variable may be displayed and changed by using the and commands. Some of the variables are Boolean, that is, the shell does not care what their value is, only whether they are set or not. Some operations treat variables numerically. The at sign command permits numeric calculations to be performed and the result assigned to a variable. The null string is considered to be zero, and any subsequent words of multi-word values are ignored. After the input line is aliased and parsed, and before each command is executed, variable expansion is performed keyed by the dollar sign character. Variable expansion can be prevented by preceding the dollar sign with a backslash character except within double quotes where substitution occurs. Variables are never expanded if enclosed in single quotes. Strings quoted by single quotes are interpreted later (see so variable substitution does not occur there until later, if at all. A dollar sign is passed unchanged if followed by a blank, tab, or end-of-line. Input/output redirections are recognized before variable expansion, and are variable expanded separately. Otherwise, the command name and entire argument list are expanded together. Unless enclosed in double quotes or given the modifier, the results of variable substitution may eventually be command and file name sub- stituted. Within double quotes, a variable whose value consists of multiple words expands to a portion of a single word, with the words of the variable's value separated by blanks. When the modifier is applied to a substitution, the variable expands to multiple words with each word separated by a blank and quoted to prevent later command or file name substitution. The following metasequences are provided for introducing variable values into the shell input. Except as noted, it is an error to refer- ence a variable that is not set. When interpreted, this sequence is replaced by the words of the value of the variable variable_name, each separated by a blank. Braces insulate variable_name from subse- quent characters that would otherwise be interpreted to be part of the variable name itself. If variable_name is not a variable, but is set in the environment, that value is used. variables cannot be modified as shown below. This modification selects only some of the words from the value of variable_name. The selector is subjected to variable substitution, and can consist of a single number or two numbers separated by a dash. The first word of a variable's value is numbered If the first number of a range is omitted it defaults to If the last member of a range is omitted it defaults to the total number of words in the variable An asterisk metacharacter used as a selector selects all words. This form gives the number of words in the variable, and is useful for forms using a [selector] option. This form substitutes the name of the file from which command input is being read. An error occurs if the file name is not known. This form is equivalent to an indexed selection from the variable This is equivalent to selecting all of argv The modifiers and can be applied to the substitutions above, as can and If curly braces appear in the command form, the modifiers must appear within the braces. The current implementation allows only one modifier on each expansion. The following substitutions cannot be modified with modifiers: Substitutes the string if variable_name is set, if it is not. Substitutes if the current input file name is known, if it is not. Substitutes the (decimal) process number of the (parent) shell. Substitutes a line from the standard input, with no further interpretation thereafter. It can be used to read from the keyboard in a shell script. Pre-Defined and Environment Variables The following variables have special meaning to the shell. Of these and are always set by the shell. Except for and this setting occurs only at initialization (initial execution of These variables are not modified unless modified explicitly by the user. copies the HP-UX environment variable into the shell variable the environment variable into the environment variable into and into copies these values back into the environment whenever the variables are reset. In a windowed environment, if detects that the window has changed size, sets the environment variables and to match the new window size. This variable is set to the arguments of the command statement. It is from this variable that positional parameters are substituted; i.e., is replaced by etc. This variable gives a list of alternate directories searched to find subdirectories in chdir commands. This variable contains the absolute path name of the current working directory. Whenever changing directories (using cd), this variable is updated. This variable is set by the command line option. If set, all built-in commands and their arguments are echoed to the standard output device just before being executed. Built-in commands are echoed before command and file name substitution, since these substitu- tions are then done selectively. For non-built-in commands, all expansions occur before echoing. This variable is used to create the command history buffer and to set its size. If this variable is not set, no command history is maintained and history substitutions cannot be made. Very large values of can cause shell memory overflow. Values of 10 or 20 are normal. All commands, exe- cutable or not, are saved in the command history buffer. This variable contains the absolute path name to your home directory. The variable is initialized from the HP-UX environment. File name expansion of tilde refers to this variable. If set, ignores end-of-file characters from input devices that are terminals. exits normally when it encounters the end-of- file condition typed as the first character on a command line). Setting ignoreeof prevents the current shell from being killed by an accidental However, to prevent an infinite loop of EOF input, terminates if it receives 26 consec- utive EOFs. This variable contains a list of the files where checks for your mail. periodically (default is 10 minutes) checks this variable before producing a prompt upon com- mand completion. If the variable contains a file name that has been modified since the last check (resulting from mail being put in the file), prints If the first word of the value of is numeric, that number specifies a different mail checking interval in seconds. If multiple mail files are specified, the shell says file_name, where file_name is the file containing the mail. This variable places restrictions on output redirection to ensure that regular files are not accidentally destroyed, and that commands using append redirection refer to existing files. If set, file name expansion is inhibited. This is most useful in shell scripts that are not dealing with file names, or after a list of file names has been obtained and further expansions are not desirable. If set, it is no longer an error for a file name expansion to not match any existing files. If there is no match, the primitive pattern is returned. It is still an error for the primitive pattern to be malformed. For example, still gives an error. If set, notifies you immediately (through your standard output device) of background job completions. The default is (indi- cate job completions just before printing a prompt). Each word of the path variable specifies a directory in which commands are to be sought for execution. A null word specifies your current working directory. If there is no path variable, only full path names can be executed. When path is not set and when users do not specify full path names, searches for the command through the directories (current directory) and A which is given neither the nor the option normally hashes the contents of the directories in the variable after reading and each time the variable is reset. If new commands are added to these directories while the shell is active, it is necessary to execute for to access these new commands. This variable lets you select your own prompt character string. The prompt is printed before each command is read from an interactive terminal input. If a appears in the string, it is replaced by the current command history buffer event number unless a preceding is given. The default prompt is the percent sign for users and the character for the super-user. The number of lines from the history list that are saved in when the user logs out. Large values for slow down the during startup. This variable contains the name of the file in which the program resides. This variable is used in forking shells to interpret files that have their execute bits set but which are not executable by the system. (See the description of This variable contains the status value returned by the last command. If the command terminated abnormally, 0200 is added to the status variable's value. Built-in commands which termi- nated abnormally return exit status and all other built-in commands set status to This variable contains a numeric value that controls the automatic timing of commands. If set, prints, for any command taking more than the specified num- ber of cpu seconds, a line of information to the standard output device giving user, system, and real execution times plus a utilization percentage. The utilization percentage is the ratio of user plus system times to real time. This message is printed after the command finishes execution. This variable is set by the command line option. If set, the words of each command are printed on the standard output device after history sub- stitutions have been made. Command and File name Substitution The remaining substitutions, command and file name substitution, are applied selectively to the arguments of built-in commands. This means that portions of expressions that are not evaluated are not subjected to these expansions. For commands which are not internal to the shell, the command name is substituted separately from the argument list. This occurs very late, after input-output redirection is per- formed, and in a child of the main shell. Command Substitution Command substitution is indicated by a command enclosed in grave accents The output from such a command is normally broken into separate words at blanks, tabs and newlines, with null words being discarded; this text then replacing the original string. Within double quotes, only newlines force new words; blanks and tabs are preserved. In any case, the single final newline does not force a new word. Note that it is thus possible for a command substitution to yield only part of a word, even if the command outputs a complete line. File name Substitution Each command word is processed as a pattern for file name substitution, also known as and replaced with a sorted list of file names which match the pattern. The form of the patterns is the Pattern Matching Notation defined by regexp(5) with the following exceptions: o Non-matching lists in bracket expressions are not supported. o In a list of words specifying file name substitution it is an error for no pattern to match an existing file name, but it is not required for each pattern to match. o The metanotation a{b,c,d}e is a shorthand for "abe ace ade". Left to right order is preserved, with results of matches being sorted separately at a low level to preserve this order. This construct may be nested. Thus: expands to whether or not these files exist, without any chance of error if the home directory for is Similarly, might expand to (Note that was not sorted with the results of matching As a special case, and are passed undisturbed. Input/Output The standard input and standard output of a command can be redirected with the following syntax: Open file name (which is first variable, command and file name expanded) as the standard input. Read the shell input up to a line which is identical to word. word is not subjected to variable, file name or command substitution, and each input line is compared to word before any substitutions are done on this input line. Unless a quoting or appears in word, variable and command sub- stitution is performed on the intervening lines, allowing to quote and Commands which are substituted have all blanks, tabs, and newlines preserved, except for the final newline which is dropped. The resultant text is placed in an anonymous temporary file which is given to the command as standard input. The file name is used as standard output. If the file does not exist, it is created; if the file exists, it is truncated, and its previous contents are lost. If the variable is set, the file must not exist or be a character special file (e.g., a terminal or or an error results. This helps prevent accidental destruction of files. In this case the exclamation point forms can be used to suppress this check. Note that the test is only applied to regular files, not to named pipes or other file types. The forms involving the ampersand character route the standard error into the specified file as well as the standard output. name is expanded in the same way as < input file names are. Uses file name as standard output the same as but appends output to the end of the file. If the variable is set, it is an error for the file not to exist unless one of the forms is given. Otherwise, it is similar to A command receives the environment in which the shell was invoked as modified by the input-output parameters and the presence of the com- mand in a pipeline. Thus, unlike some previous shells, commands executed from a shell script have no access to the text of the commands by default; rather they receive the original standard input of the shell. The mechanism should be used to present inline data. This permits shell scripts to function as components of pipelines and allows the shell to block-read its input. Diagnostic output can be directed through a pipe with the standard output. Simply use the form rather than by itself. CSH UTILITIES File Name Completion In typing file names as arguments to commands, it is no longer necessary to type a complete name, only a unique abbreviation is necessary. When you want the system to try to match your abbreviation, press the ESC key. The system then completes the file name for you, echoing the full name on your terminal. If the abbreviation does not match an available file name, the terminal's bell is sounded. The file name may be partially completed if the prefix matches several longer file names. In this case, the name is extended up to the ambiguous devia- tion, and the bell is sounded. File name completion works equally well when other directories are addressed. In addition, the tilde convention for home directories is understood in this context. Viewing a File or Directory List At any point in typing a command, you can request "what files are available" or "what files match my current specification". Thus, when you have typed: you may wish to know what files or subdirectories exist (in without aborting the command you are typing. Typing at this point lists the files available. Files are listed in multicolumn format, sorted by column. Directories and executable files are identified by a trailing and respectively. Once printed, the command is re-echoed for you to complete. Additionally, you may want to know which files match a pre- fix, the current file specification so far. If you had typed: followed by a all files and subdirectories whose prefix was in the directory would be printed. Notice that the example before was simply a degenerate case of this with a null trailing file name. (The null string is a prefix of all strings.) Notice also that a trailing slash is required to pass to a new sub-directory for both file name completion and listing. Note that the degenerate case prints a full list of login names on the current system. Command Name Recognition Command name recognition and completion works in the same manner as file name recognition and completion above. The current value of the environment variable is used in searching for the command. For example might expand to Also, lists all commands (along that begin with As an option, if the shell variable is set, a number indicating the index in is printed next to each command on a [Control]-[D] listing. Autologout A new shell variable has been added called If the terminal remains idle (no character input) at the shell's top level for a number of min- utes greater than the value assigned to you are automatically logged off. The feature is temporarily disabled while a command is execut- ing. The initial value of is 600. If unset or set to 0, is entirely disabled. Command Line Control A re-prints the current command line; erases the last word entered on the current command line. Sanity C shell restores your terminal to a sane mode if it appears to return from some command in raw, cbreak, or noecho mode. Saving Your History Buffer has the ability to save your history list between login sessions. If the shell variable is set to a number, that number of command events from your history list is saved. For example, placing the line in your file maintains a history buffer of length 10 and saves the entire list when you logout. When you log back in, the entire buffer is restored. The commands are saved in the file in your login directory. EXTERNAL INFLUENCES
Environment Variables determines the collating sequence used in evaluating pattern matching notation for file name substitution. determines the interpretation of text as single and/or multi-byte characters, the classification of characters as letters, and the charac- ters matched by character class expressions in pattern matching notation. determines the language in which messages are displayed. If or is not specified in the environment or is set to the empty string, the value of is used as a default for each unspecified or empty variable. If is not specified or is set to the empty string, a default of "C" (see lang(5)) is used instead of If any internationalization variable contains an invalid setting, behaves as if all internationalization variables are set to "C". See environ(5). when defined, enables to execute scripts that are larger than 1 GB. International Code Set Support Single- and multi-byte character code sets are supported. WARNINGS
The file should be structured such that it cannot generate any output on standard output or standard error, including occasions when it is invoked without an affiliated terminal. rcp(1) causes to be sourced, and any output generated by this file, even to standard error causes problems. Commands such as stty(1) should be placed in not in so that their output cannot affect rcp(1). has certain limitations. Words or environment variables can be no longer than 10240 bytes. The system limits argument lists to 10240 bytes. The number of arguments to a command which involves file name expansion is limited to one-sixth the number of bytes allowed in an argument list. Command substitutions may substitute no more bytes than are allowed in an argument list. To detect looping, the shell restricts the number of substitutions on a single line to 20. When a command is restarted from a stop, prints the directory it started in if it is different from the current directory; this can be mis- leading (i.e., wrong) because the job may have changed directories internally. Shell built-in functions are not stoppable/restartable. Command sequences of the form are also not handled gracefully when stopping is attempted. If you interrupt the shell then immediately executes This is especially noticeable if this expansion results from an It suf- fices to place the sequence of commands in parentheses to force it into a subshell; i.e., Because of the signal handling required by csh, interrupts are disabled just before a command is executed, and restored as the command begins execution. There may be a few seconds delay between when a command is given and when interrupts are recognized. Control over tty output after processes are started is primitive; perhaps this will inspire someone to work on a good virtual terminal interface. In a virtual terminal interface much more interesting things could be done with output control. Alias substitution is most often used to clumsily simulate shell procedures; shell procedures should be provided rather than aliases. Commands within loops, prompted for by are not placed in the history list. Control structure should be parsed rather than being recognized as built-in commands. This would allow control commands to be placed anywhere, to be combined with and to be used with and metasyntax. It should be possible to use the modifiers on the output of command substitutions. All and more than one modifier should be allowed on substitutions. Terminal type is examined only the first time you attempt recognition. To list all commands on the system along enter The csh metasequence does not work. In an international environment, character ordering is determined by the setting of rather than by the binary ordering of character values in the machine collating sequence. This brings with it certain attendant dangers, particularly when using range expressions in file name generation patterns. For example, the command, might be expected to match all file names beginning with a lowercase alphabetic character. However, if dictionary ordering is specified by it would also match file names beginning with an uppercase character (as well as those beginning with accented letters). Conversely, it would fail to match letters collated after in languages such as Norwegian. The correct (and safe) way to match specific character classes in an international environment is to use a pattern of the form: This uses to determine character classes and works predictably for all supported languages and codesets. For shell scripts produced on non-internationalized systems (or without consideration for the above dangers), it is recommended that they be executed in a non-NLS envi- ronment. This requires that etc., be set to "C" or not set at all. implements command substitution by creating a pipe between itself and the command. If the root file system is full, the substituted com- mand cannot write to the pipe. As a result, the shell receives no input from the command, and the result of the substitution is null. In particular, using command substitution for variable assignment under such circumstances results in the variable being silently assigned a NULL value. Relative path changes (such as when in a symbolically linked directory, cause knowledge of the working directory to be along the symbolic path instead of the physical path. Prior to HP-UX Release 9.0, when getting its input from a file, would exit immediately if unable to execute a command (such as if it was unable to find the command). Beginning at Release 9.0, continues on and attempts to execute the remaining commands in the file. However, if the old behavior is desired for compatibility purposes, set the environment variable to 1. When is defined, the shell retains as little input as possible in memory. Thus, certain constructs like that involve rewinding of the shell's input, may not work properly. Non-interactive shells will not read the file at the beginning of execution. If required by the script, the file needs to be read explic- itly, using the command. AUTHOR
was developed by the University of California, Berkeley and HP. FILES
A csh script sourced (executed) at the beginning of execution by each shell. See A csh script sourced (executed) by login shell, after at login. A csh script read at the beginning of the execution by an interactive shell. See A csh script sourced (executed) by login shell, at logout. Source of home directories for Standard shell, for shell scripts not starting with a A csh script sourced (executed) before and when starting a csh login (analogous to in the POSIX shell). Temporary file for SEE ALSO
cd(1), echo(1), kill(1), nice(1), sh(1), umask(1), access(2), exec(2), fork(2), pipe(2), umask(2), wait(2), a.out(4), environ(5), lang(5), regexp(5), tty(7). tutorial in csh(1)

Featured Tech Videos