/bin/[

[Matthew Seaman]

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Jim Stapleton wrote:
> Sorry if you get this question a lot - a few searches didn't find
> results for me.
> 
> I have a "/bin/[" file in my system - I just want to make sure it's
> not a sign of someone having hacked my machine.

No -- that's perfectly alright.  If you look closely you can see
that it is in fact identical to /bin/test:

% ls -lai test '['
871508 -r-xr-xr-x  2 root  wheel  7652 Aug 18 12:31 [*
871508 -r-xr-xr-x  2 root  wheel  7652 Aug 18 12:31 test*

It's used for testing various conditions in shell scripts -- like
this for example:

   [ "x$foo" != "x" ] && echo "\$foo is set to $foo"

which could be written equivalently as:

   test "x$foo" != "x" && echo 2\$foo is set to $foo"

The curious name is historic, based on some early shells where there
was a built-in syntax using the '[' character.  Having test or [ as
an external program means that all the standard shell on FreeBSD can
 use exactly the same test syntax and theres only one copy of the
code to keep maintained in the source tree.

	Cheers,

	Matthew
	
- --
Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                  Flat 3
PGP: http://www.infracaninophile.co.uk/pgpkey     Ramsgate
                                                  Kent, CT11 9PW
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