Just Curious: why do "/usr/bin/test" and "/usr/bin/[" have different sizes?

DaneM · 01-04-2014, 05:26 PM

This isn't a pressing concern, but I just had a "WTF?!" moment and thought I should share the love.

Code:

dane@orchestrator ~ $ which [
/usr/bin/[
dane@orchestrator ~ $ ls -lh `which [`
-rwxr-xr-x 1 root root 35K Nov 19  2012 /usr/bin/[*
dane@orchestrator ~ $ ls -lh `which test`
-rwxr-xr-x 1 root root 31K Nov 19  2012 /usr/bin/test*
dane@orchestrator ~ $ dpkg-query -S /usr/bin/[
coreutils: /usr/bin/[
dane@orchestrator ~ $ dpkg-query -S /usr/bin/test
coreutils: /usr/bin/test

So...how does this work?

(Have fun!)

--Dane

astrogeek · 01-04-2014, 05:53 PM

Because they are not the identical.

That sounds like a tautology, but it is not.

Among their differences are their usage syntax and the fact that [ honors --help and --version options while test does not.

So while we speak and think of them as being the same thing, they really are not (at least the GNU versions).

DaneM · 01-05-2014, 07:20 AM

Are there functional differences, other than --help and --version?

anon237 · 01-05-2014, 07:46 AM

A heads up about test, test and [ (yep, test is mentioned twice).

There is also a bash internal command called test, which is actually used when not using the full path to the test binary (/usr/bin/test). See man bash, the SHELL BUILTIN COMMANDS section.

The binary [ and binary test work the same way (except for the --version/--help), as you might have noticed both point to the saem manual page.

The binary and the build in do have some differences (availability and names of options).

DaneM · 01-06-2014, 12:54 AM

Ah, excellent distinction! Thanks, druuna.

mina86 · 01-06-2014, 03:33 AM

Take a look at source code of test and [ for yourself. The only difference starts at line 837.

The reason test does not recognise any options is that it would not be possible to distinguish whether the option was actual option or a test. I.e. “test "$FOO"” is a valid way to test whether the variable FOO is empty or not, however if FOO was “--help” or “--version”, the test would result in superfluous output.

[ can support options since its valid invocation requires “]” at the end of the command.

Quote:

Originally Posted by druuna

There is also a bash internal command called test, which is actually used when not using the full path to the test binary (/usr/bin/test). See man bash, the SHELL BUILTIN COMMANDS section.

There is also a bash built-in “[” (which does not support “--help” or “--version” by the way).

PS. This of course does not change the fact that both binaries could be the same and the behaviour could be changed based on “argv[0]”. I assume this is not the cases to speed things up slightly.