8.9 Built-in Commands

@ [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 Section 8.5 earlier in this chapter. Two special forms are also valid:

@ variable++

Increment variable by 1.

@ variable--

Decrement variable by 1.

#

Ignore all text that follows on the same line. # is used in shell scripts as the comment character and is not really a command.

#!shell

Used as the first line of a script to invoke the named shell (with optional arguments) or other program. 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 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 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 Section 8.6.7.

Examples

Set the size for 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 totals of used and free memory.

bg [jobIDs]

Put the current job or the jobIDs in the background.

Example

To place a time-consuming process in the background, you might begin with:

4% nroff -ms report 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 a command.

Options

-a

List standard and alternate key bindings.

-b key

Expect key to be one of the following: a control character (in hat notation, e.g., ^B, or C notation, e.g., C-B); a metacharacter (e.g., M-B); a function key (e.g., F-string); or an extended prefix key (e.g., X-B).

-c command

Interpret command as a shell, not editor, command.

-d key

Bind key to its original binding.

-e

Bind to standard Emacs bindings.

-k key

Expect key to refer to an arrow (left, right, up, or down).

-l

List and describe all editor commands.

-r key

Completely unbind key.

-s

Interpret command as a literal string and treat as terminal input.

-u

Print usage message.

-v

Bind to standard vi bindings.

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.

case pattern :

Identify a pattern in a switch.

cd [options] [dir]

Change working directory to dir. Default is user's home directory. If dir is a relative pathname but is not in the current directory, the cdpath variable is searched. See the sample .tcshrc file earlier in this chapter.

Options

-

Change to previous directory.

-l

Explicitly expand ~ notation; implies -p.

-n

Wrap entries before end-of-line; implies -p.

-p

Print directory stack.

-v

Print entries one per line; implies -p.

chdir [dir]

Same as cd. Useful if you are redefining cd.

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

c

Complete current word only, without referring to pattern.

C

Complete current word only, referring to pattern.

n

Complete previous word.

N

Complete word before previous word.

p

Expect pattern to be a range of numbers. Perform completion within that range.

Options for list

Various lists of strings can be searched for possible completions. Some list options include:

(string)

Members of the list string

$variable

Words from variable

`command`

Output from command

a

Aliases

b

Bindings

c

Commands

C

External (not built-in) commands

d

Directories

D

Directories whose names begin with string

e

Environment variables

f

Filenames

F

Filenames that begin with string

g

Groups

j

Jobs

l

Limits

n

Nothing

s

Shell variables

S

Signals

t

Text files

T

Text files whose names begin with string

u

Users

v

Any variables

x

Like n, but prints select as an explanation with the editor command list-choices

X

Completions

select

select 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

-c

Clear the directory stack.

-l

Expand the home directory symbol (~) to the actual directory name.

-n

Wrap output.

-v

Print one directory per line.

-L file

Re-create stack from file, which should have been created by dirs -S file.

-S file

Print to file a series of pushd and popd commands that can be invoked to replicate the stack.

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 3 and Chapter 7.

echotc [options] arguments

Display terminal capabilities or move cursor on screen, depending on the argument.

Options

-s

Return empty string, not error, if capability doesn't exist.

-v

Display verbose messages.

Arguments

baud

Display current baud rate.

cols

Display current column.

cm column row

Move cursor to specified coordinates.

home

Move cursor to home position.

lines

Print number of lines per screen.

meta

Does this terminal have meta capacity (usually the Alt key)?

tabs

Does this terminal have tab capacity?

else

Reserved word for interior of if ... endif statement.

end

Reserved word that ends a foreach or switch 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.)

Examples

The following line 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

Another example of eval can be found under alias.

exec command

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.

Example

If 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 Section 8.5.1.5 earlier in this chapter for the list of file-test operators.

foreach name (wordlist)    commandsend

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).

Examples

Rename all files that begin with a capital letter:

% foreach i ([A-Z]*)
? mv $i $i.new
? 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. No \ escapes are recognized in its expansion, 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 character 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 Section 8.6.)

Options

-c

Clear history list.

-h

Print history list without event numbers.

-r

Print in reverse order; show oldest commands last.

n

Display only the last n history commands, instead of the number set by the history shell variable.

-L file

Load series of pushd and popd commands from file in order to re-create a saved stack.

-M file

Merge the current directory stack and the stack saved in file. Save both, sorted by time, in file as a series of pushd and popd commands.

-S file

Print to file a series of pushd and popd commands that can be invoked to replicate the stack.

-T

Print with timestamp.

Example

To 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. By default, configure shell script to exit on hangup signal.

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. (Redirection 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 Section 8.5 earlier in this chapter, or the shift or while commands.

Example

Take 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 /bin/kill described in Chapter 3 but also allows symbolic job names. Stubborn processes can be killed using signal 9.

Options

-l

List the signal names. (Used by itself.)

-signal, -s signal

The signal number or name without the SIG prefix (e.g., HUP, not SIGHUP). The command kill -l prints a list of the available signal names. The list varies by system architecture; for a PC-based system, it looks like this:

% kill -l
HUP INT QUIT ILL TRAP ABRT BUS FPE KILL USR1 SEGV USR2
PIPE ALRM TERM STKFLT CHLD CONT STOP TSTP TTIN TTOU URG 
XCPU XFSZ VTALRM PROF WINCH POLL PWR SYS RTMIN RTMIN+1
RTMIN+2 RTMIN+3 RTMAX-3 RTMAX-2 RTMAX-1 RTMAX

The signals and their numbers are defined in /usr/include/asm/signal.h; look in that file to find the signals that apply to your system.

Examples

If you've issued the following command:

44% nroff -ms report &

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 limits are shown or set; with -h, hard limits are used. A hard limit imposes an absolute limit that can't be exceeded. Only a privileged user may raise it. See also unlimit.

Option

-h

Use hard, not current, limits.

Resources

coredumpsize

Maximum size of a core dump file.

cputime

Maximum number of seconds the CPU can spend; can be abbreviated as cpu.

datasize

Maximum size of data (including stack).

descriptors

Maximum number of open files.

filesize

Maximum size of any one file.

maxproc

Maximum number of processes.

memorylocked

Maximum size a process can lock into memory.

memoryuse

Maximum amount of physical memory that can be allocated to a process.

vmemoryuse

Maximum amount of virtual memory that can be allocated to a process.

stacksize

Maximum size of stack.

Limit

A number followed by an optional character (a unit specifier).

For cputime:	nh (for n hours)
	nm (for n minutes)
	mm:ss (minutes and seconds)
For others:	nk (for n kilobytes, the default)
	nm (for n megabytes)

log

Consult the watch variable for list of users being watched. Print list of those who are presently logged in.

login [user|-p]

Replace user's login shell with /bin/login. -p is used to preserve environment variables.

logout

Terminate the login shell.

ls-F [options] [files]

Faster alternative to ls -F. If given any options, invokes ls.

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 3.) The priority range is -20 to 20, with a default of 4. The range seems backward: -20 gives the highest priority (fastest execution); 20 gives the lowest. Only a privileged user may specify a negative number.

+n

Add n to the priority value (lower job priority).

-n

Subtract n from the priority value (raise job priority). Privileged users only.

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 3.)

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 bash's trap 2 and trap "" 2 commands). 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 -.

Example

onintr 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 (or the nth entry) from the directory stack and print the stack that remains. The current entry has number 0 and appears on the left. See also dirs and pushd.

Options

+n

Specify nth entry.

-l

Expand ~ notation.

-n

Wrap long lines.

-p

Override the pushdsilent shell variable, which otherwise prevents the printing of the final stack.

-v

Print precisely one directory per line.

printenv [variable]

Print all (or one specified) environment variables and their values.

pushd name
pushd [options]
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 0.) With no arguments, pushd switches the first two entries and changes to the new current directory. The +n, -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 directory to PATH before rehashing.) See also unhash.

repeat n command

Execute n instances of command.

Examples

Print three copies of memo:

% repeat 3 pr memo | lp

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

+hh:mm

Schedule event to take place hh:mm from now.

-n

Remove nth item from schedule.

set variable=value
set [options] variable[n]=value
set variableset

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 nth 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 "Predefined Shell Variables" earlier in this chapter. Only one of -f or -l can be given.

Options

-f

Set only the first occurrence of a variable to keep it unique.

-l

Set only the last occurrence of a variable to keep it unique.

-r

List only read-only variables, or set specified variable to read-only.

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 is 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. setenv is not necessary for the PATH variable, which is automatically exported from path.

settc capability value

Set terminal capability to value.

setty [options] [+|-mode]

Do not allow shell to change specified tty modes. By default, act on the execute set.

Options

+mode

Without arguments, list all modes in specified set that are on. Otherwise, turn on specified mode.

-mode

Without arguments, list all modes in specified set that are off. Otherwise, turn off specified mode.

-a

List all modes in specified set.

-d

Act on the edit set of modes (used when editing commands).

-q

Act on the quote set of modes (used when entering characters verbatim).

-x

Act on the execute set of modes (used when executing examples). This is the default.

shift [variable]

If variable is given, shift the words in a wordlist variable; i.e., name[2] becomes name[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.

Example

while ($#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 ~/.cshrc

stop jobIDs

Stop the background jobs specified by jobIDs; this is the complement of Ctrl-Z or suspend.

suspend

Suspend the current foreground job; same as Ctrl-Z. Often used to stop an su command.

switch

Process commands depending on the value of a variable. When you need to handle more than three choices, switch is a useful alternative to an if-then-else statement. If the string variable matches pattern1, the first set of commands is executed; if string matches pattern2, the second set of commands is executed; and so on. If no patterns match, execute commands under the default case. string can be specified using command substitution, variable substitution, or filename expansion. Patterns can be specified using the pattern matching symbols *, ?, and [ ]. breaksw is used to exit the switch. If breaksw is omitted (which is rarely done), the switch continues to execute another set of commands until it reaches a breaksw or endsw. Following 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.

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.

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. This command can be run 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 variable

Remove an environment variable. Filename matching is not valid. 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-ins, and executables named command found in the path.

which command

Report which version of command will be executed. Same as the 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.

Example

set 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