NAME

shell_builtins − shell command interpreter built-in functions

DESCRIPTION

The shell command interpreters ( sh(1), csh(1), and ksh(1)), have special built-in functions which are interpreted by the shell as commands.  Many of these built-in commands are implemented by more than one of the shells, and some are unique to a particular shell.  These are:

Bourne Shell, sh,  Special Commands

Input/output redirection is now permitted for these commands.  File descriptor 1 is the default output location.  When Job Control is enabled, additional Special Commands are added to the shell’s environment. 

Additional to these built-in reserved command words, sh also uses:

: No effect; the command does nothing.  A zero exit code is returned. 

. filename
Read and execute commands from filename and return.  The search path specified by PATH is used to find the directory containing filename.

C shell, csh

Built-in commands are executed within the C shell.  If a built-in command occurs as any component of a pipeline except the last, it is executed in a subshell.  Additional to these built-in reserved command words, csh also uses:

: Null command.  This command is interpreted, but performs no action. 

Korn Shell, ksh,  Special Commands

Input/Output redirection is permitted.  Unless otherwise indicated, the output is written on file descriptor 1 and the exit status, when there is no syntax error, is zero. 

Commands that are preceded by one or two † (daggers) are treated specially in the following ways:

1.  Variable assignment lists preceding the command remain in effect when the command completes. 

2.  I/O redirections are processed after variable assignments. 

3.  Errors cause a script that contains them to abort. 

4.  Words, following a command preceded by †† that are in the format of a variable assignment, are expanded with the same rules as a variable assignment.  This means that tilde substitution is performed after the = sign and word splitting and file name generation are not performed. 

Additional to these built-in reserved command words, ksh also uses:

† : [ arg ... ]
The command only expands parameters.

† . file [ arg ... ]
Read the complete file then execute the commands.  The commands are executed in the current shell environment.  The search path specified by PATH is used to find the directory containing file. If any arguments arg are given, they become the positional parameters.  Otherwise the positional parameters are unchanged.  The exit status is the exit status of the last command executed.  the loop termination test. 

SEE ALSO

alias(1), break(1), case(1), cd(1), chmod(1), csh(1), echo(1), exec(1), exit(1), for(1), find(1), function(1), getoptcvt(1) getopts(1), glob(1), hash(1), history(1), if(1), intro(1), jobs(1), kill(1), ksh(1), let(1), limit(1), login(1), logout(1), newgrp(1), nice(1), nohup(1), print(1), pwd(1), read(1), readonly(1), repeat(1), set(1), sh(1), shift(1), suspend(1), test(1B), time(1), times(1), trap(1), typeset(1), umask(1), wait(1), while(1), chdir(2), chmod(2), creat(2), umask(2), getopt(3C), profile(4), environ(5)

SunOS 5.5  —  Last change: 1 Feb 1995