What is this file: /usr/bin/[

ia64processor · 01-29-2007, 07:16 AM

ls -al /usr/bin/[
-rwxr-xr-x 1 root root 31048 Jan 11 00:06 /usr/bin/[

This file can also be found in FC5 as well. Just curious...

raskin · 01-29-2007, 07:44 AM

It is executable similar or identical to 'test' executable. It is invoked when you use constructs like 'if [ -f file ]; then echo yes; fi;'. Here '[' is just a command name, not a special syntax character.

colucix · 01-29-2007, 07:48 AM

Raskin told that! As a proof you can safely do

Code:

/usr/bin/[ --help

Nick_Battle · 01-29-2007, 08:07 AM

Strictly, I think that command only exists for use by shells where the "[" command isn't a shell builtin - eg. in bash, writing "if [ ..." doesn't run the /usr/bin/[ program, but other shells might need it.

bash-2.03$ type [
[ is a shell builtin
bash-2.03$

raskin · 01-29-2007, 08:17 AM

I would add that it is so in bash invoked as bash, and not /bin/sh which often links to /bin/bash. And it can be used not only by shells, but also by any other programs... I am not sure if POSIX requires providing executable capable to handle 'test' invocation.

ia64processor · 02-04-2007, 02:17 AM

Thank you all gentlemen!