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3.4 Common Features

The following table displays features that are common to the Bourne, Korn, and C shells. Note that the Korn shell is an enhanced version of the Bourne shell; therefore, the Korn shell includes all features of the Bourne shell, plus some others. The commands bg , fg , jobs , stop , and suspend are available only on systems that support job control. (Essentially all modern Unix systems do.)

Symbol/Command Meaning/Action
> Redirect output.
>> Append to file.
< Redirect input.
<< "Here" document (redirect input).
| Pipe output.
|& Start a coprocess. Korn shell only.
& Run process in background.
; Separate commands on same line.
* Match any character(s) in filename.
? Match single character in filename.
[ ] Match any characters enclosed.
( ) Execute in subshell.
` ` Substitute output of enclosed command.
" " Partial quote (allows variable and command expansion).
' ' Full quote (no expansion).
\ Quote following character.
$ var Use value for variable.
$$ Process ID.
$0 Command name.
$ n n th argument (0 <= n <= 9).
$* All arguments as simple words.
# Begin comment.
bg Background execution.
break Break from loop statements.
cd Change directory.
continue Resume a program loop.
echo Display output.
eval Evaluate arguments.
exec Execute a new shell.
fg Foreground execution.
jobs Show active jobs.
kill Terminate running jobs.
shift Shift positional parameters.
stop Suspend a background job.
suspend Suspend a foreground job (such as a shell created by su ).
time Time a command.
umask Set default file permissions for new files.
unset Erase variable or function definitions.
wait Wait for a background job to finish.

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