if($thestring =~/13/) { print "13 is in the string"; }

##</code><code>##

if("13" =~ /13,130,213/) { print "13 is in the string"; }

##</code><code>##

my $thestring = "13,130,213";
my $thecheck  = "13";
if($thestring =~ /$thecheck/){ print "$thecheck is in $thestring\n"; }