## cat p.pl ; perl p.pl

#  This is "grep -f" like.

use v5.10.0; use strict;

my @in =
  ( "polka\n"
  , "avoid redding dot me\n"
  , "dot me\n"
  , "yellow\n"
  );
my $find  = 'me';
my $avoid = 'avoid';

for my $ignore ( $avoid , undef )
{
  process_input( $find , $ignore , @in );
  print "- - - -\n";
}
exit;


sub process_input
{
  my ( $grep , $skip , @in ) = @_;

  my $show;
  while ( my $line = shift @in )
  {
    $show =
      find( $grep , $line )
      &&
      ( defined $skip ? ! find ( $skip , $line ) : 1 )
      ;
  }
  continue
  {
    $show and print $line;
  }

  return;
}

sub find
{
  my ( $find , $line ) = @_;

  defined $find && defined $line
    or return;

  my @break = split '' , $find;
  my $size  = scalar @break;

  my $start = 0;
  my ( @seen );
  for my $c ( @break )
  {
    my $i = index $line , $c , $start;

    $i == -1 || scalar @seen == $size
      and last;

    push @seen , $i;

    if ( scalar @seen > 1 )
    {
      $seen[-1] - $seen[-2] == 1 or last;
    }

    $start = $i + 1;
  }

  return scalar @seen == $size
}

__END__
dot me
- - - -
avoid redding dot me
dot me
- - - -
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