my $ext = "js";
my $String = "abc.js";
print "ok" if($String =~ '[^/]*\.$ext');
# or:
print "ok2" if($String =~ m=[^/]*\.$ext=);
# or:
print "ok3" if($String =~ m"[^/]*\.$ext");
# or:
print "ok4" if($String =~ m![^/]*\.$ext!);
# or:
print "ok5" if($String =~ m{[^/]*\.$ext});