5.9. Built-in Commands
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@ variable = expression @ variable[n] = expression @ Assign the value of the arithmetic expression to variable, or to the nth element of variable if the index n is specified. With no variable or expression specified, print the values of all shell variables (same as set). Expression operators as well as examples are listed under the section "Expressions," earlier in this chapter. Two special forms are also valid:
# Ignore all text that follows on the same line. # is used in shell scripts as the comment character and is not really a command. In addition, a file that has # as its first character is sometimes interpreted by older systems as a C shell script.
#! shell Used as the first line of a script to invoke the named shell. Anything given on the rest of the line is passed as a single argument to the named shell. This feature is typically implemented by the kernel, but may not be supported on some older systems. Some systems have a limit of around 32 characters on the maximum length of shell. Any program that interprets input may be used for shell, such as awk or Perl. For example: #! /bin/tcsh -f
: Null command. Returns an exit status of 0. The colon command is often put as the first character of a Bourne or Korn shell script to act as a place-holder to keep a # (hash) from accidentally becoming the first character.
alias [name [command]] Assign name as the shorthand name, or alias, for command. If command is omitted, print the alias for name; if name also is omitted, print all aliases. Aliases can be defined on the command line, but more often they are stored in .tcshrc so that they take effect upon logging in. (See the section "Sample .tcshrc File" earlier in this chapter.) Alias definitions can reference command-line arguments, much like the history list. Use \!* to refer to all command-line arguments, \!^ for the first argument, \!\!:2 for the second, \!$ for the last, and so on. An alias name can also be any valid Unix command except alias or unalias; however, you lose the original command's meaning unless you type \name. See also unalias and the earlier section "Special Aliases." ExamplesSet the size for xterm windows under the X Window System: alias R 'set noglob; eval 'resize'; unset noglob' Show aliases that contain the string "ls": alias | grep ls Run nroff on all command-line arguments: alias ms 'nroff -ms \!*' Copy the file that is named as the first argument: alias back 'cp \!^ \!^.old' Use the regular ls, not its alias: % \ls
alloc Print total amount of used and free memory.
bg [jobIDs] Put the current job or the jobIDs in the background. See the earlier section "Job Control." ExampleTo place a time-consuming process in the background, you might begin with: 4% nroff -ms report | col > report.txt CTRL-Z and then issue any one of the following: 5% bg 5% bg % Current job 5% bg %1 Job number 1 5% bg %nr Match initial string nroff 5% % &
bindkey [options] [key] [command] Display all key bindings, or bind a key to an editor command. Options
break Resume execution following the end command of the nearest enclosing while or foreach.
breaksw Break from a switch; continue execution after the endsw.
built-ins Print all built-in shell commands.
bye Same as logout. Must have been compiled into the shell; see the version variable.
case pattern: Identify a pattern in a switch.
cd [options] [dir] Change working directory to dir; default is home directory of user. If dir is a relative pathname but is not in the current directory, the cdpath variable is searched. See the section "Sample .tcshrc File" earlier in this chapter. Options
chdir [dir] Same as cd. Useful if you are redefining cd as an alias.
complete [string [word/pattern/list[:select]/[suffix]]] List all completions, or, if specified, all completions for string (which may be a pattern). Further options can be specified. Options for word
Options for listVarious lists of strings can be searched for possible completions. Some list options include:
selectselect should be a glob pattern. Completions are limited to words that match this pattern. suffix is appended to all completions.
continue Resume execution of nearest enclosing while or foreach.
default: Label the default case (typically last) in a switch.
dirs [options] Print the directory stack, showing the current directory first. See also popd and pushd. Options
echo [-n] string Write string to standard output; if -n is specified, the output is not terminated by a newline. Set the echo_style shell variable to emulate BSD and/or System V echo flags and escape sequences. See also echo in Chapter 2 and Chapter 4.
echotc [options] arguments Display terminal capabilities or move cursor on screen, depending on the argument. Options
Arguments
else Reserved word for interior of if ... endif statement.
end Reserved word that ends a foreach or while statement.
endif Reserved word that ends an if statement.
endsw Reserved word that ends a switch statement.
eval args Typically, eval is used in shell scripts, and args is a line of code that may contain shell variables. eval forces variable expansion to happen first and then runs the resulting command. This "double scanning" is useful any time shell variables contain input/output redirection symbols, aliases, or other shell variables. (For example, redirection normally happens before variable expansion, so a variable containing redirection symbols must be expanded first using eval; otherwise, the redirection symbols remain uninterpreted.) A Bourne shell example can be found under eval in Chapter 4. A tcsh example of eval can be found under alias. Other uses of eval are shown next. ExamplesThe following lines can be placed in the .login file to set up terminal characteristics: set noglob eval 'tset -s xterm' unset noglob The following commands show the effect of eval: % set b='$a' % set a=hello % echo $b Read the command line once $a % eval echo $b Read the command line twice hello
exec command [args ...] Execute command in place of current shell. This terminates the current shell, rather than creating a new process under it.
exit [expr] Exit a shell script with the status given by expr. A status of zero means success; nonzero means failure. If expr is not specified, the exit value is that of the status variable. exit can be issued at the command line to close a window (log out).
fg [jobIDs] Bring the current job or the jobIDs to the foreground. jobID can be %job-number. See also the section "Job Control" earlier in this chapter. ExampleIf you suspend a vi editing session (by pressing CTRL-Z), you might resume vi using any of these commands: % % % fg % fg % % fg %vi Match initial string
filetest -op files Apply op file-test operator to files. Print results in a list. See the section "File inquiry operators" earlier in this chapter for the list of file-test operators.
foreach name (wordlist) commands end Assign variable name to each value in wordlist and execute commands between foreach and end. You can use foreach as a multiline command issued at the shell prompt (first of the following examples), or you can use it in a shell script (second example). ExamplesRename all files that begin with a capital letter: % foreach i ([A-Z]*) foreach? mv $i $i.old foreach? end Check whether each command-line argument is an option or not: foreach arg ($argv) # does it begin with - ? if ("$arg" =~ -*) then echo "Argument is an option" else echo "Argument is a filename" endif end
glob wordlist Do filename, variable, and history substitutions on wordlist. This expands it much like echo, except that no \ escapes are recognized, and words are delimited by null characters. glob is typically used in shell scripts to "hardcode" a value so that it remains the same for the rest of the script.
goto string Skip to a line whose first nonblank word is string followed by a colon, and continue execution below that line. On the goto line, string can be a variable or filename pattern, but the label branched to must be a literal, expanded value and must not occur within a foreach or while.
hashstat Display statistics that show the hash table's level of success at locating commands via the path variable.
history [options] Display the list of history events. (History syntax is discussed earlier in the section "Command History.") Note: multiline compound commands such as foreach ... end are not saved in the history list. In general, the interactive command-line editing facilities are preferable to those of history and history substitution with the ! character. Options
ExampleTo save and execute the last five commands: history -h 5 > do_it source do_it
hup [command] Start command but make it exit when sent a hangup signal, which is sent when shell exits. With no arguments, set the shell to exit on hangup signal. This latter form is allowed only in scripts.
if Begin a conditional statement. The simple format is: if (expr) cmd There are three other possible formats, shown side by side: if (expr) then if (expr) then if (expr) then cmds cmds1 cmds1 endif else else if (expr) then cmds2 cmds2 endif else cmds3 endif In the simplest form, execute cmds if expr is true, otherwise do nothing. (Even if expr is false, any redirection in cmd still occurs; this is a bug.) In the other forms, execute one or more commands. If expr is true, continue with the commands after then; if expr is false, branch to the commands after else or else if and continue checking. For more examples, see the section "Expressions" earlier in this chapter, or the shift or while commands. ExampleTake a default action if no command-line arguments are given: if ($#argv == 0) then echo "No filename given. Sending to Report." set outfile = Report else set outfile = $argv[1] endif
jobs [-l] List all running or stopped jobs; -l includes process IDs. For example, you can check whether a long compilation or text format is still running. Also useful before logging out.
kill [options] IDs Terminate each specified process ID or job ID. You must own the process or be a privileged user. This built-in is similar to the external kill command described in Chapter 2 but also allows symbolic job names. See the kill entry in Chapter 2 for a list of commonly available signals and for the header files where the corresponding signal numbers may be found. Stubborn processes can be killed using signal 9. See also the earlier section "Job Control." Options
ExamplesIf you've issued the following command: 44% nroff -ms report > report.txt & [1] 19536 tcsh prints job and process IDs you can terminate it in any of the following ways: 45% kill 19536 Process ID 45% kill % Current job 45% kill %1 Job number 1 45% kill %nr Initial string 45% kill %?report Matching string
limit [-h] [resource [limit]] Display limits or set a limit on resources used by the current process and by each process it creates. If no limit is given, the current limit is printed for resource. If resource also is omitted, all limits are printed. By default, the current soft limits are shown or set; with -h, hard limits are used. A soft limit may be increased or decreased without requiring special privileges. A hard limit imposes an absolute limit that can't be exceeded. Only a privileged user may raise it. See also unlimit. Option
Resources
LimitA number followed by an optional character (a unit specifier).
log Consult the watch variable for list of users being watched. Print list of those who are presently logged in.
login [options] [user] Replace a login shell with /bin/login. See the entry for login in Chapter 2 and your system's login manpage.
logout Terminate the login shell.
ls-F [options] [files] Faster alternative to ls -F. If given any options, invokes ls. See also the listlinks variable.
newgrp [-] [group] Change user's group ID to specified group ID or, if none is specified, to original group ID. If - is entered as an option, reset environment as if user had logged in with new group. Must have been compiled into the shell; see the version variable.
nice [±n] command Change the execution priority for command or, if none is given, change priority for the current shell. (See also nice in Chapter 2.) The priority range is -20 to 19, with a default of 4. The range is backwards from what you might expect: -20 gives the highest priority (fastest execution); 19 gives the lowest. Only a privileged user may specify a negative number.
nohup [command] "No hangup signals." Do not terminate command after terminal line is closed (i.e., when you hang up from a phone or log out). Use without command in shell scripts to keep script from being terminated. (See also nohup in Chapter 2.)
notify [jobID] Report immediately when a background job finishes (instead of waiting for you to exit a long editing session, for example). If no jobID is given, the current background job is assumed.
onintr label onintr - onintr "On interrupt." Used in shell scripts to handle interrupt signals (similar to the TRap 2 and TRap "" 2 commands in the Bourne shell). The first form is like a goto label. The script will branch to label: if it catches an interrupt signal (e.g., CTRL-C). The second form lets the script ignore interrupts. This is useful at the beginning of a script or before any code segment that needs to run unhindered (e.g., when moving files). The third form restores interrupt handling previously disabled with onintr -. Exampleonintr cleanup Go to "cleanup" on interrupt . . Shell script commands . cleanup: Label for interrupts onintr - Ignore additional interrupts rm -f $tmpfiles Remove any files created exit 2 Exit with an error status
popd [options] Remove the current entry from the directory stack or remove the n th entry from the stack. The current entry has number zero and appears on the left. See also dirs and pushd. Options
printenv [variable] Print all (or one specified) environment variables and their values.
pushd [options] name pushd [options] +n pushd The first form changes the working directory to name and adds it to the directory stack. The second form rotates the nth entry to the beginning, making it the working directory. (Entry numbers begin at zero.) With no arguments, pushd switches the first two entries and changes to the new current directory. The -l, -n, and -v options behave the same as in popd. See also dirs and popd. Examples% dirs /home/bob /usr % pushd /etc Add /etc to directory stack /etc /home/bob /usr % pushd +2 Switch to third directory /usr /etc /home/bob % pushd Switch top two directories /etc /usr /home/bob % popd Discard current entry; go to next /usr /home/bob
rehash Recompute the internal hash table for the path variable. Use rehash whenever a new command is created during the current session. This allows the path variable to locate and execute the command. (If the new command resides in a directory not listed in path, add the directory to path before rehashing.) See also unhash.
repeat n command Execute n instances of command. ExamplesGenerate a test file for a program by saving 25 copies of /usr/dict/words in a file: % repeat 25 cat /usr/dict/words > test_file Read 10 lines from the terminal and store in item_list: % repeat 10 line > item_list Append 50 boilerplate files to report: % repeat 50 cat template >> report
sched [options] sched time command Without options, print all scheduled events. The second form schedules an event. time should be specified in hh:mm form (e.g., 13:00). Options
set [-r] variable = value set [-r] variable[n] = value set [-f | -l] variable=(list) set [-r] variable set [-r] Set variable to value or, if multiple values are specified, set the variable to the list of words in the value list. If an index n is specified, set the n th word in the variable to value. (The variable must already contain at least that number of words.) If only variable is specified, set the variable to null. With no arguments, display the names and values of all set variables. See also the section "Predefined Shell Variables," earlier in this chapter. Only one of -f or -l can be given. Options
Examples% set list=(yes no maybe) Assign a wordlist % set list [3 ]=maybe Assign an item in existing wordlist % set quote="Make my day" Assign a variable % set x=5 y=10 history=100 Assign several variables % set blank Assign a null value to blank
setenv [name [value]] Assign a value to an environment variable name. By convention, name should be uppercase. value can be a single word or a quoted string. If no value is given, the null value is assigned. With no arguments, display the names and values of all environment variables. A number of environment variables are automatically exported from the corresponding shell variables; see the earlier section "Environment Variables."
settc capability value Set terminal capability to value.
setty [options] [±mode] Do not allow shell to change specified tty modes. There are three sets of modes, edit, quote, and execute. By default, act on the execute set. Options
shift [variable] If variable is given, shift the words in a word list variable; e.g., assuming a wordlist variable named offices, offices[2] becomes offices[1]. With no argument, shift the positional parameters (command-line arguments); i.e., $2 becomes $1. shift is typically used in a while loop. See additional example under while. Examplewhile ($#argv) While there are arguments if (-f $argv[1]) wc -l $argv[1] else echo "$argv[1] is not a regular file" endif shift Get the next argument end
source [-h] script [args] Read and execute commands from a shell script. With -h, the commands are added to the history list but aren't executed. Arguments can be passed to the script and are put in argv. Example% source ~/.tcshrc
stop jobIDs Stop the background jobs specified by jobIDs; this is the complement of CTRL-Z or suspend.
suspend Suspend the current foreground job; similar to CTRL-Z. Often used to stop an su command.
switch Process commands depending on a string value. When you need to handle more than three choices, switch is a useful alternative to an if-then-else statement. If the string matches pattern1, the first set of commands executes; if string matches pattern2, the second set of commands executes; and so on. If no patterns match, the set of commands under the default case executes. string can be specified using command substitution, variable substitution, or filename expansion. Patterns can be specified using the pattern-matching symbols *, ?, [, and ]. breaksw exits the switch after commands are executed. If breaksw is omitted (which is rarely done), the switch continues to execute another set of commands until it reaches a breaksw or endsw. Here is the general syntax of switch, side-by-side with an example that processes the first command-line argument. switch (string) switch ($argv[1]) case pattern1: case -[nN]: commands nroff $file | lp breaksw breaksw case pattern2: case -[Pp]: commands pr $file | lp breaksw breaksw case pattern3: case -[Mm]: commands more $file breaksw breaksw . case -[Ss]: . sort $file . breaksw default: default: commands echo "Error no such option" exit 1 breaksw breaksw endsw endsw
telltc Print all terminal capabilities and their values.
termname [termtype] Check the termcap or terminfo database to see if termtype exists. With no argument, use the current value of the TERM variable. This command prints the termtype to standard output and returns zero if the terminal type is found in the database, one otherwise.
time [command] Execute a command and show how much time it uses. With no argument, time can be used in a shell script to time the script.
umask [nnn] Display file-creation mask or set file-creation mask to octal nnn. The file-creation mask determines which permission bits are turned off. With no nnn, print the current mask. See the umask entry in Chapter 2 for examples.
unalias pattern Remove all aliases whose names match pattern from the alias list. See alias for more information.
uncomplete pattern Remove completions (specified by complete) whose names match pattern.
unhash Stop using the internal hash table. The shell stops using hashed values and searches the path directories to locate a command. See also rehash.
unlimit [-h] [resource] Remove the allocation limits on resource. If resource is not specified, remove limits for all resources. See limit for more information. With -h, remove hard limits. Removing hard limits can be done only by a privileged user.
unset variables Remove one or more variables. Variable names may be specified as a pattern, using filename metacharacters. Does not remove read-only variables. See set.
unsetenv variables Remove one or more environment variables. Variable names may be specified as a pattern, using filename metacharacters. See setenv.
wait Pause in execution until all child processes complete, or until an interrupt signal is received.
watchlog Same as log. Must have been compiled into the shell; see the version shell variable.
where command Display all aliases, built-in commands, and executables named command found in the path.
which command Report which version of command will be executed. Same as the external executable which, but faster, and checks tcsh built-ins.
while (expression) commands end As long as expression is true (evaluates to nonzero), evaluate commands between while and end. break and continue can be used to terminate or continue the loop. See also the example under shift. Exampleset user = (alice bob carol ted) while ($argv[1] != $user[1]) Cycle through each user, checking for a match shift user If we cycled through with no match... if ($#user == 0) then echo "$argv[1] is not on the list of users" exit 1 endif end |
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