sub search
{
     my ($PartNumber) = @_;

     while (<FILE>)
     {
          if ($main::fields[0] eq $PartNumber)
          {
                # ...
                return 1;   # Ends search() function
          }
     }
     close(FILE);

     return;  # Returns empty handed
}

##</code><code>##

$|++;

my $what;
do
{
     print "PartNumber? ";
     chomp($what = <STDIN>);
} while (!search($what));