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PerlIO-Layers-0.004
River stage two • 5 direct dependents • 32 total dependents
2 ++
/ PerlIO::Layers

NAME

PerlIO::Layers - Querying your filehandle's capabilities

VERSION

Version 0.004

SYNOPSIS

 use PerlIO::Layers qw/query_handle/;

 if (!query_handle(\*STDOUT, binary)) {
     ...
 }

DESCRIPTION

Perl's filehandles are implemented as a stack of layers, with the bottom-most usually doing the actual IO and the higher ones doing buffering, encoding/decoding or transformations. PerlIO::Layers allows you to query the filehandle's properties concerning there layers.

SUBROUTINES

query_handle($fh, $query_name)

This query a filehandle for some information. Currently supported queries include:

  • utf8

    Check whether the filehandle handles unicode

  • crlf

    Check whether the filehandle does crlf translation

  • binary

    Check whether the filehandle is binery. This test is pessimistic (for unknown layers it will assume it's not binary).

  • buffered

    Check whether the filehandle is buffered.

  • readable

    Check whether the filehandle is readable.

  • writeable

    Check whether the filehandle is writeable.

  • open

    Check whether the filehandle is open.

  • temp

    Check whether the filehandle refers to a temporary file.

get_layers($fh)

Gets information on the layers of a filehandle. It's a list with whose entries have 3 elements: the name of the layer, the arguments of the layer (may be undef) and an arrayref with the flags of the layer as strings. The flags array can contain any of these values.

  • EOF

    End of file has been reached.

  • CANWRITE

    Writes are permitted, i.e. opened as ">" or "+<" or ">>", etc.

  • CANREAD

    Reads are permitted i.e. opened "<" or "+>".

  • ERROR

    An error has occurred.

  • TRUNCATE

    Truncate file suggested by open mode.

  • APPEND

    All writes should be appends.

  • CRLF

    Layer is performing Win32-like "\n" mapped to CR,LF for output and CR,LF mapped to "\n" for input. Normally the provided "crlf" layer is the only layer that need bother about this. binmode will mess with this flag rather than add/remove layers if the PERLIO_K_CANCRLF bit is set for the layers class.

  • UTF8

    Data written to this layer should be UTF-8 encoded; data provided by this layer should be considered UTF-8 encoded. Can be set on any layer by ":utf8" dummy layer. Also set on ":encoding" layer.

  • UNBUF

    Layer is unbuffered - i.e. write to next layer down should occur for each write to this layer.

  • WRBUF

    The buffer for this layer currently holds data written to it but not sent to next layer.

  • RDBUF

    The buffer for this layer currently holds unconsumed data read from layer below.

  • LINEBUF

    Layer is line buffered. Write data should be passed to next layer down whenever a "\n" is seen. Any data beyond the "\n" should then be processed.

  • TEMP

    File has been unlink()ed, or should be deleted on close().

  • OPEN

    Handle is open.

  • FASTGETS

    This instance of this layer supports the "fast gets " interface. Normally set based on PERLIO_K_FASTGETS for the class and by the existence of the function(s) in the table. However a class that normally provides that interface may need to avoid it on a particular instance. The "pending" layer needs to do this when it is pushed above a layer which does not support the interface.

query_handle provides a more high level interface to this, you should probably use that when you can.

AUTHOR

Leon Timmermans, <leont at cpan.org>

BUGS

Please report any bugs or feature requests to bug-perlio-layers at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=PerlIO-Layers. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

SUPPORT

You can find documentation for this module with the perldoc command.

    perldoc PerlIO::Layers

You can also look for information at:

LICENSE AND COPYRIGHT

Copyright 2010 Leon Timmermans.

This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License.

See http://dev.perl.org/licenses/ for more information.