POE::Filter::Line(3pm)

1POE::Filter::Line(3)  User Contributed Perl Documentation POE::Filter::Line(3)
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NAME

6       POE::Filter::Line - serialize and parse terminated records (lines)
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SYNOPSIS

9         #!perl
10
11         use POE qw(Wheel::FollowTail Filter::Line);
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13         POE::Session->create(
14           inline_states => {
15             _start => sub {
16               $_[HEAP]{tailor} = POE::Wheel::FollowTail->new(
17                 Filename => "/var/log/system.log",
18                 InputEvent => "got_log_line",
19                 Filter => POE::Filter::Line->new(),
20               );
21             },
22             got_log_line => sub {
23               print "Log: $_[ARG0]\n";
24             }
25           }
26         );
27
28         POE::Kernel->run();
29         exit;
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DESCRIPTION

32       POE::Filter::Line parses stream data into terminated records.  The
33       default parser interprets newlines as the record terminator, and the
34       default serializer appends network newlines (CR/LF, or "\x0D\x0A") to
35       outbound records.
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37       Record terminators are removed from the data POE::Filter::Line returns.
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39       POE::Filter::Line supports a number of other ways to parse lines.
40       Constructor parameters may specify literal newlines, regular
41       expressions, or that the filter should detect newlines on its own.
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PUBLIC FILTER METHODS

44       POE::Filter::Line's new() method has some interesting parameters.
45
46   new
47       new() accepts a list of named parameters.
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49       In all cases, the data interpreted as the record terminator is stripped
50       from the data POE::Filter::Line returns.
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52       "InputLiteral" may be used to parse records that are terminated by some
53       literal string.  For example, POE::Filter::Line may be used to parse
54       and emit C-style lines, which are terminated with an ASCII NUL:
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56         my $c_line_filter = POE::Filter::Line->new(
57           InputLiteral => chr(0),
58           OutputLiteral => chr(0),
59         );
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61       "OutputLiteral" allows a filter to put() records with a different
62       record terminator than it parses.  This can be useful in applications
63       that must translate record terminators.
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65       "Literal" is a shorthand for the common case where the input and output
66       literals are identical.  The previous example may be written as:
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68         my $c_line_filter = POE::Filter::Line->new(
69           Literal => chr(0),
70         );
71
72       An application can also allow POE::Filter::Line to figure out which
73       newline to use.  This is done by specifying "InputLiteral" to be undef:
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75         my $whichever_line_filter = POE::Filter::Line->new(
76           InputLiteral => undef,
77           OutputLiteral => "\n",
78         );
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80       "InputRegexp" may be used in place of "InputLiteral" to recognize line
81       terminators based on a regular expression.  In this example, input is
82       terminated by two or more consecutive newlines.  On output, the
83       paragraph separator is "---" on a line by itself.
84
85         my $paragraph_filter = POE::Filter::Line->new(
86           InputRegexp => "([\x0D\x0A]{2,})",
87           OutputLiteral => "\n---\n",
88         );
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PUBLIC FILTER METHODS

91       POE::Filter::Line has no additional public methods.
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BUGS

100       The default input newline parser is a regexp that has an unfortunate
101       race condition.  First the regular expression:
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103         /(\x0D\x0A?|\x0A\x0D?)/
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105       While it quickly recognizes most forms of newline, it can sometimes
106       detect an extra blank line.  This happens when a two-byte newline
107       character is broken between two reads.  Consider this situation:
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109         some stream dataCR
110         LFother stream data
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112       The regular expression will see the first CR without its corresponding
113       LF.  The filter will properly return "some stream data" as a line.
114       When the next packet arrives, the leading "LF" will be treated as the
115       terminator for a 0-byte line.  The filter will faithfully return this
116       empty line.
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118       It is advised to specify literal newlines or use the autodetect feature
119       in applications where blank lines are significant.
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AUTHORS & COPYRIGHTS

122       Please see POE for more information about authors and contributors.
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126perl v5.12.1                      2010-04-03              POE::Filter::Line(3)