You escaped the 'any character' period, so it becomes a literal period. Try this instead:

#!/usr/bin/perl
if ($ARGV[0] =~ m/^ep_svr_\d+_[A-Za-z]{3}_[A-Za-z]{3}_.+\z/x) {
    print "valid label: $ARGV[0]\n";
    }
else {
    print "invalid label: $ARGV[0]\n";
    };
__END__
$ epsrv.pl ep_svr_12_abc_abc_theend
valid label: ep_svr_12_abc_abc_theend
[download]

So, at least for my limited test case, it works.

CU
Robartes-