my @output = `./retrive 2301`;

##</code><code>##

my $cid="";
foreach (@output)
{ if ($_ =~/^CID: (.*)/)
  { $cid=$1; 
  }
}

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;
my @output = `./retrive 2301`;
my $cid="";
my $r_regex = qr/^CID: (.*)/;
foreach (@output)
{ if ($_ =~ $r_regex)
  { $cid=$1; 
  }
}