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.\" ========================================================================
.\"
.IX Title "POE::Filter::Grep 3pm"
.TH POE::Filter::Grep 3pm "2020-02-07" "perl v5.30.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
POE::Filter::Grep \- select or remove items based on simple rules
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&  #!perl
\&
\&  use POE qw(
\&    Wheel::FollowTail
\&    Filter::Line Filter::Grep Filter::Stackable
\&  );
\&
\&  POE::Session\->create(
\&    inline_states => {
\&      _start => sub {
\&        my $parse_input_as_lines = POE::Filter::Line\->new();
\&
\&        my $select_sudo_log_lines = POE::Filter::Grep\->new(
\&          Put => sub { 1 },
\&          Get => sub {
\&            my $input = shift;
\&            return $input =~ /sudo\e[\ed+\e]/i;
\&          },
\&        );
\&
\&        my $filter_stack = POE::Filter::Stackable\->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\->new(
\&          Filename => "/var/log/system.log",
\&          InputEvent => "got_log_line",
\&          Filter => $filter_stack,
\&        );
\&      },
\&      got_log_line => sub {
\&        print "Log: $_[ARG0]\en";
\&      }
\&    }
\&  );
\&
\&  POE::Kernel\->run();
\&  exit;
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
POE::Filter::Grep 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 \fBgrep()\fR function.
.PP
POE::Filter::Grep is designed to be combined with other filters
through POE::Filter::Stackable.  In the \*(L"\s-1SYNOPSIS\*(R"\s0 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 \s-1DO\s0 mention sudo.)
.SH "PUBLIC FILTER METHODS"
.IX Header "PUBLIC FILTER METHODS"
In addition to the usual POE::Filter methods, POE::Filter::Grep also
supports the following.
.SS "new"
.IX Subsection "new"
\&\fBnew()\fR constructs a new POE::Filter::Grep object.  It must either be
called with a single Code 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.
.PP
.Vb 5
\&  sub reject_bidoofs {
\&    my $pokemon = shift;
\&    return 1 if $pokemon ne "bidoof";
\&    return;
\&  }
\&
\&  my $gotta_catch_nearly_all = POE::Filter::Grep\->new(
\&    Code => \e&reject_bidoofs,
\&  );
.Ve
.PP
Enforce read-only behavior:
.PP
.Vb 4
\&  my $read_only = POE::Filter::Grep\->new(
\&    Get => sub { 1 },
\&    Put => sub { 0 },
\&  );
.Ve
.SS "modify"
.IX Subsection "modify"
\&\fBmodify()\fR changes a POE::Filter::Grep object's behavior at run-time.
It accepts the same parameters as \fBnew()\fR, and it replaces the existing
tests with new ones.
.PP
.Vb 5
\&  # Don\*(Aqt give away our Dialgas.
\&  $gotta_catch_nearly_all\->modify(
\&    Get => sub { 1 },
\&    Put => sub { return shift() ne "dialga" },
\&  );
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
POE::Filter for more information about filters in general.
.PP
POE::Filter::Stackable for more details on stacking filters.
.SH "BUGS"
.IX Header "BUGS"
None known.
.SH "AUTHORS & COPYRIGHTS"
.IX Header "AUTHORS & COPYRIGHTS"
The Grep filter was contributed by Dieter Pearcey.  Documentation is
provided by Rocco Caputo.
.PP
Please see the \s-1POE\s0 manpage for more information about authors and
contributors.