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Script to print first and last line have two pattern
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POE::Filter::Line(3pm) User Contributed Perl Documentation POE::Filter::Line(3pm) NAME
POE::Filter::Line - serialize and parse terminated records (lines) SYNOPSIS
#!perl use POE qw(Wheel::FollowTail Filter::Line); POE::Session->create( inline_states => { _start => sub { $_[HEAP]{tailor} = POE::Wheel::FollowTail->new( Filename => "/var/log/system.log", InputEvent => "got_log_line", Filter => POE::Filter::Line->new(), ); }, got_log_line => sub { print "Log: $_[ARG0] "; } } ); POE::Kernel->run(); exit; DESCRIPTION
POE::Filter::Line parses stream data into terminated records. The default parser interprets newlines as the record terminator, and the default serializer appends network newlines (CR/LF, or "x0Dx0A") to outbound records. Record terminators are removed from the data POE::Filter::Line returns. POE::Filter::Line supports a number of other ways to parse lines. Constructor parameters may specify literal newlines, regular expressions, or that the filter should detect newlines on its own. PUBLIC FILTER METHODS
POE::Filter::Line's new() method has some interesting parameters. new new() accepts a list of named parameters. In all cases, the data interpreted as the record terminator is stripped from the data POE::Filter::Line returns. "InputLiteral" may be used to parse records that are terminated by some literal string. For example, POE::Filter::Line may be used to parse and emit C-style lines, which are terminated with an ASCII NUL: my $c_line_filter = POE::Filter::Line->new( InputLiteral => chr(0), OutputLiteral => chr(0), ); "OutputLiteral" allows a filter to put() records with a different record terminator than it parses. This can be useful in applications that must translate record terminators. "Literal" is a shorthand for the common case where the input and output literals are identical. The previous example may be written as: my $c_line_filter = POE::Filter::Line->new( Literal => chr(0), ); An application can also allow POE::Filter::Line to figure out which newline to use. This is done by specifying "InputLiteral" to be undef: my $whichever_line_filter = POE::Filter::Line->new( InputLiteral => undef, OutputLiteral => " ", ); "InputRegexp" may be used in place of "InputLiteral" to recognize line terminators based on a regular expression. In this example, input is terminated by two or more consecutive newlines. On output, the paragraph separator is "---" on a line by itself. my $paragraph_filter = POE::Filter::Line->new( InputRegexp => "([x0Dx0A]{2,})", OutputLiteral => " --- ", ); PUBLIC FILTER METHODS
POE::Filter::Line has no additional public methods. SEE ALSO
Please see POE::Filter for documentation regarding the base interface. The SEE ALSO section in POE contains a table of contents covering the entire POE distribution. BUGS
The default input newline parser is a regexp that has an unfortunate race condition. First the regular expression: /(x0Dx0A?|x0Ax0D?)/ While it quickly recognizes most forms of newline, it can sometimes detect an extra blank line. This happens when a two-byte newline character is broken between two reads. Consider this situation: some stream dataCR LFother stream data The regular expression will see the first CR without its corresponding LF. The filter will properly return "some stream data" as a line. When the next packet arrives, the leading "LF" will be treated as the terminator for a 0-byte line. The filter will faithfully return this empty line. It is advised to specify literal newlines or use the autodetect feature in applications where blank lines are significant. AUTHORS &; COPYRIGHTS Please see POE for more information about authors and contributors. perl v5.14.2 2012-05-15 POE::Filter::Line(3pm)
