The easiest way is to do that using WMI. A bit of Googling tells me that you can get the command line of any process using WMIC:

WMIC PROCESS get Caption,Commandline,Processid
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Then, you just have to go through all lines in your script and you have the process id.

See perlop for how to get the output of another process.

Maybe you want to use DBD::WMI to avoid running an external program. Most likely, the SQL would be

SELECT
    Caption
  , CommandLine
  , ProcessId
FROM
    Win32_PROCESS
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Take a look at the Win32::Process::List module, it's probably all you need. Alternatively, you could get away with a simple

 
my @proc_lines = `tasklist`;
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but then you would have to parse the lines for the relevant info yourself. Win32::Process::List does that already.

UPDATE: A small example from the module documentation:

use warnings;
use strict;
use Win32::Process::List;

my $plist = Win32::Process::List->new();
my $pid = $plist->GetProcessPid("explorer");
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Windows tasklist command only has the image name of the process, not its complete commandline. There can many process with same image name. Also, the Win32::Process::List module has image name not the commandline of the process.

I'm not even certain one can begin to respond to this since a) there is no context given and b) it's technically not even a question but a statement. The answer (if it is a question) might be as simple as don't bother looking in the process list but instead look at $$.