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bash Pocket Reference
book

bash Pocket Reference

by Arnold Robbins
May 2010
Beginner to intermediate content levelBeginner to intermediate
130 pages
3h 20m
English
O'Reilly Media, Inc.
Content preview from bash Pocket Reference

Command Execution

When you type a command, Bash looks in the following places until it finds a match:

  1. Keywords such as if and for.

  2. Aliases. You can’t define an alias whose name is a shell keyword, but you can define an alias that expands to a keyword, e.g., alias aslongas=while. When not in POSIX mode, Bash does allow you to define an alias for a shell keyword.

  3. Special built-ins like break and continue. The list of POSIX special built-ins is . (dot), :, break, continue, eval, exec, exit, export, readonly, return, set, shift, times, trap, and unset. Bash adds source.

  4. Functions. When not in POSIX mode, Bash finds functions before all built-in commands.

  5. Nonspecial built-ins such as cd and test.

  6. Scripts and executable programs, for which the shell searches in the directories listed in the PATH environment variable.

  7. When a command is not found, if a function named command_not_found_handle exists, the shell will call it, passing the command words as the function arguments.

The distinction between “special” built-in commands and nonspecial ones comes from POSIX. This distinction, combined with the command command, makes it possible to write functions that override shell built-ins, such as cd. For example:

cd () {                   Shell function; found before built-in cd
    command cd "$@"       Use real cd to change directory
    echo now in $PWD      Other stuff we want to do
}

If Bash exits due to receiving SIGHUP, or if the huponexit shell option is set, Bash will send a SIGHUP to all running child jobs. Use disown -h to prevent ...

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Publisher Resources

ISBN: 9781449388669Errata Page