open(SuitDoc,<STDIN>) || die "Cannot open file";
...
   while ($line = <SuitDoc>) {
      ...

##</code><code>##

while (<>) {  # read from file name(s) in @ARGV or from pipe
    ...

##</code><code>##


use strict;  # get into this habit

my $suits = 'hearts|clubs|spades|diamonds';

while (<>) {
    if ( /($suits)/ ) {
        print $1;
    }
}