Command Execution
When you type a command, Bash looks in the following places until it finds a match:
Keywords such as
if
andfor
.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.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.
Functions. When not in POSIX mode, Bash finds functions before all built-in commands.
Nonspecial built-ins such as cd and test.
Scripts and executable programs, for which the shell searches in the directories listed in the
PATH
environment variable.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 ...
Get bash Pocket Reference now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.