$ echo 'CME.b/ESM8' | grep -P '^CME\.b?[^/.]'
CME.b/ESM8

##</code><code>##

#!/usr/bin/perl

use strict;
use warnings;

my $string = 'CME.b/ESM8';

if ( $string =~ /^CME\.b?[^\/.]/ )
{
	print "yes\n";
}
else {
	print "no\n";
}