# perldoc > POE::Filter::Grep

## NAME
    [POE::Filter::Grep](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter%3A%3AGrep/markdown) - select or remove items based on simple rules

## SYNOPSIS
      #!perl

      use POE qw(
        [Wheel::FollowTail](https://www.chedong.com/phpMan.php/perldoc/Wheel%3A%3AFollowTail/markdown)
        [Filter::Line](https://www.chedong.com/phpMan.php/perldoc/Filter%3A%3ALine/markdown) [Filter::Grep](https://www.chedong.com/phpMan.php/perldoc/Filter%3A%3AGrep/markdown) [Filter::Stackable](https://www.chedong.com/phpMan.php/perldoc/Filter%3A%3AStackable/markdown)
      );

      [POE::Session](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3ASession/markdown)->create(
        inline_states => {
          _start => sub {
            my $parse_input_as_lines = [POE::Filter::Line](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter%3A%3ALine/markdown)->new();

            my $select_sudo_log_lines = [POE::Filter::Grep](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter%3A%3AGrep/markdown)->new(
              Put => sub { 1 },
              Get => sub {
                my $input = shift;
                return $input =~ /sudo\[\d+\]/i;
              },
            );

            my $filter_stack = [POE::Filter::Stackable](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter%3A%3AStackable/markdown)->new(
              Filters => [
                $parse_input_as_lines, # first on get, last on put
                $select_sudo_log_lines, # first on put, last on get
              ]
            );

            $_[HEAP]{tailor} = [POE::Wheel::FollowTail](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AWheel%3A%3AFollowTail/markdown)->new(
              Filename => "/var/log/system.log",
              InputEvent => "got_log_line",
              Filter => $filter_stack,
            );
          },
          got_log_line => sub {
            print "Log: $_[ARG0]\n";
          }
        }
      );

      [POE::Kernel](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AKernel/markdown)->run();
      exit;

## DESCRIPTION
    [POE::Filter::Grep](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter%3A%3AGrep/markdown) selects or removes items based on simple tests. It may be used to filter
    input, output, or both. This filter is named and modeled after Perl's built-in grep() function.

    [POE::Filter::Grep](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter%3A%3AGrep/markdown) is designed to be combined with other filters through [POE::Filter::Stackable](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter%3A%3AStackable/markdown).
    In the "SYNOPSIS" example, a filter stack is created to parse logs as lines and remove all
    entries that don't pertain to a sudo process. (Or if your glass is half full, the stack only
    selects entries that DO mention sudo.)

## PUBLIC FILTER METHODS
    In addition to the usual [POE::Filter](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter/markdown) methods, [POE::Filter::Grep](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter%3A%3AGrep/markdown) also supports the following.

  new
### new
    parameter, or both a Put and a Get parameter. The values for Code, Put, and Get are code
    references that, when invoked, return true to select an item or false to reject it. A Code
    function will be used for both input and output, while Get and Put functions allow input and
    output to be filtered in different ways. The item in question will be passed as the function's
    sole parameter.

      sub reject_bidoofs {
        my $pokemon = shift;
        return 1 if $pokemon ne "bidoof";
        return;
      }

      my $gotta_catch_nearly_all = [POE::Filter::Grep](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter%3A%3AGrep/markdown)->new(
        Code => \&reject_bidoofs,
      );

    Enforce read-only behavior:

      my $read_only = [POE::Filter::Grep](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter%3A%3AGrep/markdown)->new(
        Get => sub { 1 },
        Put => sub { 0 },
      );

  modify
### modify
    parameters as new(), and it replaces the existing tests with new ones.

      # Don't give away our Dialgas.
      $gotta_catch_nearly_all->modify(
        Get => sub { 1 },
        Put => sub { return shift() ne "dialga" },
      );

## SEE ALSO
    [POE::Filter](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter/markdown) for more information about filters in general.

    [POE::Filter::Stackable](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter%3A%3AStackable/markdown) for more details on stacking filters.

## BUGS
    None known.

AUTHORS & COPYRIGHTS
    The Grep filter was contributed by Dieter Pearcey. Documentation is provided by Rocco Caputo.

    Please see the POE manpage for more information about authors and contributors.