#!/usr/bin/perl -w
use strict;

my @x =  (
            'smomedef12345',
            'anabc12345 and there is some def12345678',
            'qwerabc12345def55',
            'def87654321abc54321',
         );
          
foreach (@x)
{
   next unless (m/abc\d{5}/); #pre-condition to look further

   (my $string8) = m/def(\d{8})/;  #puts $string8 in list context
   #$string8 = (m/def(\d{8})/)[0]; #alternate way with list slice

   if ( !defined($string8) )
   {
     $string8 = 'undefined'; #Perl 5.10 has a special way to do this
                             #Probably here just do "next;"
                             # because an undefined value means the
                             # regex above did not match!
   }
   
   print "var def=$string8\n";
}
__END__
prints:
..note that first item is silently skipped!
var def=12345678
var def=undefined
var def=87654321 #note that this works even though
                 #the pre-condition of abc\d{5}
                 #occurs later in the line! Wow!

##</code><code>##

my @x =  (
            'smomedef12345',
            'anabc12345 and there is some def12345678',
            'qwerabc12345def55',
            'def87654321abc54321',
         );
        
print map{ /abc\d{5}/ and /def(\d{8})/ ? "def=$1\n" : () }@x; 
__END__
prints:
def=12345678
def=87654321