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Working with let command
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shell_builtins(1) shell_builtins(1) NAME
shell_builtins, case, for, foreach, function, if, repeat, select, switch, until, while - shell command interpreter built-in commands The shell command interpreters csh(1), ksh(1), and sh(1) have special built-in commands. The commands case, for, foreach, function, if, repeat, select, switch, until, and while are commands in the syntax recognized by the shells. They are described in the Commands section of the manual pages of the respective shells. The remaining commands listed in the table below are built into the shells for reasons such as efficiency or data sharing between command invocations. They are described on their respective manual pages. | Command | Shell alias |csh, ksh bg |csh, ksh, sh break |csh, ksh, sh case |csh, ksh, sh cd |csh, ksh, sh chdir |csh, sh continue |csh, ksh, sh dirs |csh echo |csh, ksh, sh eval |csh, ksh, sh exec |csh, ksh, sh exit |csh, ksh, sh export |ksh, sh false |ksh fc |ksh fg |csh, ksh, sh for |ksh, sh foreach |csh function |ksh getopts |ksh, sh glob |csh goto |csh hash |ksh, sh hashstat |csh history |csh if |csh, ksh, sh jobs |csh, ksh, sh kill |csh, ksh, sh let |ksh limit |csh login |csh, ksh, sh logout |csh, ksh, sh nice |csh newgrp |ksh, sh nohup |csh notify |csh onintr |csh popd |csh print |ksh pushd |csh pwd |ksh, sh read |ksh, sh readonly |ksh, sh rehash |csh repeat |csh return |ksh, sh select |ksh set |csh, ksh, sh setenv |csh shift |csh, ksh, sh source |csh stop |csh, ksh, sh suspend |csh, ksh, sh switch |csh test |ksh, sh time |csh times |ksh, sh trap |ksh, sh true |ksh type |ksh, sh typeset |ksh ulimit |ksh, sh umask |csh, ksh, sh unalias |csh, ksh unhash |csh unlimit |csh unset |csh, ksh, sh unsetenv |csh until |ksh, sh wait |csh, ksh, sh whence |ksh while |csh, ksh, sh 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. In addition 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 con- taining 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 exe- cuted in a subshell. In addition 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 * (asterisks) 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 vari- able assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not performed. In addition 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 posi- tional parameters. Otherwise, the positional parameters are unchanged. The exit status is the exit status of the last com- mand executed. the loop termination test. intro(1), alias(1), break(1), cd(1), chmod(1), csh(1), echo(1), exec(1), exit(1), find(1), getoptcvt(1), getopts(1), glob(1), hash(1), his- tory(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), read- only(1), set(1), sh(1), shift(1), suspend(1), test(1B), time(1), times(1), trap(1), typeset(1), umask(1), wait(1), chdir(2), chmod(2), creat(2), umask(2), getopt(3C), profile(4), environ(5) 29 Jun 2005 shell_builtins(1)
