[SOLVED] The special expression `-l STRING' for "test" command

Star_Gazer · 04-21-2010, 04:46 PM

I have searched and searched in regards to this documented 'special expression '-l STRING' for the 'test' command, and to no avail, have I found out why it does not work on my system.

The example always given is:

Code:

test -l abc -gt 1 && echo yes

And the returned result is:

Code:

bash: test: -l: unary operator expected

The documention is usually as follows:
Numeric tests
Numeric relationals. The arguments must be entirely numeric (possibly negative), or the special expression `-l STRING', which evaluates to the length of STRING.

Then examples are given, including the one I provided above.

Does anyone else have this issue of getting an error when trying this special expression of 'l STRING' ???

Regards,
Clifton

catkin · 04-21-2010, 05:10 PM

You are looking at the documnetation for the test command (/bin/test) but running the shell bulitin test which behaves differently. Here's /bin/test working as you expect

Code:

c@CW8:~$ /bin/test -l abc -gt 1 && echo yes
yes

Star_Gazer · 04-21-2010, 08:08 PM

Quote:

Originally Posted by catkin

You are looking at the documnetation for the test command (/bin/test) but running the shell bulitin test which behaves differently. Here's /bin/test working as you expect

Code:

c@CW8:~$ /bin/test -l abc -gt 1 && echo yes
yes

Thank you!

This issue for me is now solved.

I did not know that there was a builtin version and one that is external (not sure if that is the right word). I did a "whereis test" and found the 'test' command you are referring to.

Code:

~/Documents/Practice $ whereis test
test: /usr/bin/test /usr/bin/X11/test /usr/share/man/man1/test.1.gz

~/Documents/Practice $ /usr/bin/test -l abc -gt 1 && echo yes
yes

~/Documents/Practice $ /usr/bin/X11/test -l abc -gt 1 && echo yes
yes

Weird that there is two different 'test' commands, but at least now I know. I'll check out the "[" one as well (as I noted the file on disk in the same directories as 'test').

Thanks Again,
Clifton

grail · 04-21-2010, 09:21 PM

FYI: Just to add, if you do a man bash you will find there are a number of bash builtin equivalents:
ie test, [, echo (to name a few)

catkin · 04-22-2010, 01:40 AM

Quote:

Originally Posted by Star_Gazer

I did not know that there was a builtin version and one that is external (not sure if that is the right word).

...

Weird that there is two different 'test' commands, but at least now I know. I'll check out the "[" one as well (as I noted the file on disk in the same directories as 'test').

Yes -- "builtin" and "external" are the terms used in the shell documentation.

The concept of a shell is of a command interpreter and originally the shell itself was relatively lightweight with few builtins except for the ones that had to be such as cd. Some external commands such as test were used so heavily in shell scripting that the resource cost of having them as externals (create new process by fork, load new program by exec) reduced performance. The solution was to implement them as builtins. echo is another good example.

The original externals were left in place for backward compatibility and for use from other languages, for example C can call /bin/test and others via the system call (even if there are better ways of implementing the same functionality in C!).

For current bash programming the Conditional Construct [[ ]] is preferred to builtins test and [ (and definitely to externals test and [

) for reasons explained here.