Command Execution
When you type a command to Bash, it looks in the following places until it finds a match:
Keywords such as if and for.
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.(In non-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, source, times, trap, and unset.Functions. When in non-POSIX mode, Bash finds functions before built-in commands.
Nonspecial built-ins like cd and test.
Scripts and executable programs, for which the shell searches in the directories listed in the PATH environment variable.
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 }
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