Thanks. Now it works fine after your update. Here a sample code snippet:

#!/usr/bin/perl

use strict;
use warnings;
use SVN::Notify;

my $command = 'perl';

my $exe = SVN::Notify->find_exe($command);
if( defined $exe )
{
    print "Command \"$command\" exists!";
}
else
{
    print "Command \"$command\" does NOT exist!";
}
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Only problem is that it is not able to handle parameters. If I use the command "perl --version" then I receive the answer that this command does not exist. If I use only "perl" then I get the answer that it exists.

Fazit: Thank you a lot. This is a very good method to find out whether a command exists or not. But it is necessary to cut away the parameters of the command before giving it to the SVN::Notify->find_exe function.