Just to throw in my implementation, if I were to write this I wouldn't just give it a directory name, I'd give it an array of files, assuming I could always just use glob("*") as one of its parameters. It'd end up like this:

sub fgrep_dash_l{
  my $pattern = shift;
  my @searchfiles = @_;

  my @found;

  foreach my $file (@searchfiles){
    my $FH;
    open FH, $file or warn "error opening file $file" and next;
    while(<FH>){
      push @found,$file and last if m/$pattern/;
    }
  }
  return @found;
}
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