Why does pidof from homebrew returns always zero?

I've installed pidof via homebrew

brew install pidof

And think about two cases:

$ pidof bash > /dev/null; echo $?
$ pidof asdf > /dev/null; echo $?

The results are:

0
0

Why does it happen? Other linux throw 1 when pidof couldn't find process.

Solution 1:

The reason is that the pidof from HomeBrew is a different program than pidof in Linux. Even though they share the same name, and parts of the same functionality, they're actually quite different.

For example the HomeBrew pidof will also kill processes for you when specifying the -k argument, which Linux pidof cannot do. In contrast Linux pidof lets you specify you only want a single PID returned in single-shot mode with the -s parameter, the HomeBrew version hasn't got such an option. There are many other differences.

On Linux, pidof comes from the ubiquitous sysvinit-tools package. When you do a pidof programname in Linux, it loops through the running processes while keeping track of whether or not it found the program name you're looking for. If it doesn't find it, it returns an exit status of !0 (which is 1).

In HomeBrew, pidof is a standalone utility from "Night Productions". Their program has no source in common with the Linux pidof, and does not track whether or not it found the program name. It always returns an exit status of 0 in any case.

Solution 2:

If you look at the Homebrew formula of pidof, you will see that the Homebrew version is built from : http://www.nightproductions.net/downloads/pidof_source.tar.gz

If you look at the source code pidof.c used by Homebrew, you will see that each occurrence of the return statement in the main function, is in the form:

return 0

except one time, when the usage of the command is printed:

printf("USAGE: %s [-klvh] [PID name]\n",ProgName);
                return 1;
                break;

On the other hand, in Linux distributions, such as Debian, the pidof command is coming from the System V style init programs. If you download the source code and look at killall5.c (which is then linked to pidof), you have at the last line of the main function:

return retval;

where retvalcan be non-null.

So the main reson why the Homebrew version of pidof and the Linux version of pidof return different values is because they use different codebase.