[SOLVED] What is the program /usr/bin/[

tgrzelak · 02-03-2011, 08:15 AM

I have found this program on my RHEL 5.5 machines? What is its purpose?

-rwxr-xr-x 1 root root 32296 Jan 10 13:27 [

Thanks!

Sayan Acharjee · 02-03-2011, 08:18 AM

Quote:

Originally Posted by tgrzelak

I have found this program on my RHEL 5.5 machines? What is its purpose?

-rwxr-xr-x 1 root root 32296 Jan 10 13:27 [

Thanks!

This is test command and it is used to check file types and compare values. e.g.,

Code:

[ -f /etc/passwd ] && echo "Yes" || echo "No"

It checks if /etc/passwd exists or not.

Read the man page to know more,

Code:

#man [

or

Code:

#man test

crabboy · 02-03-2011, 08:18 AM

I have no such file on my 5.5. I'd assume someone created it with a typo.

Try to view the file, if it's binary, run strings on it and see if you can tell what it is.

edit...

Nope, I stand corrected. I do have the file.

colucix · 02-03-2011, 09:03 AM

Actually [ is both a shell built-in and a command. The same as echo. Usually built-ins have precedence over commands. You can verify this using

Code:

type [

whereas if you want to find all the available versions:

Code:

type -a [

and to find all the related stuff (e.g. man pages):

Code:

whereis [

the [ command is provided by the coreutils package. If you check the man page, as suggested above, you will see the [ command has the following synopsis:

Code:

[ EXPRESSION ]

where the last argument is a (mandatory) closing square bracket.

tgrzelak · 02-03-2011, 09:48 AM

I don't have a man page on it. But as everyone has stated, I am more comfortable now seeing that this is a legitimate program. I was worried it was a hack or an artifact of a bad line command.

Thanks!

lumak · 02-03-2011, 11:22 AM

BTW, the programs test and [ don't support "==" so if you want your bash scripts to be POSIX compatible, use "=" instead.