NAME

PerlIO::Layers - Querying your filehandle's capabilities

VERSION

version 0.010

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 these layers.

FUNCTIONS

query_handle($fh, $query_name [, $argument])

This query a filehandle for some information. All queries can take an optional argument, that will test for that layer's properties instead of all layers of the handle. Currently supported queries include:

• layer

  Check the presence of a certain layer. Unlike most other properties $argument is mandatory for this query.

• utf8

  Check whether the filehandle/layer handles unicode

• crlf

  Check whether the filehandle/layer does crlf translation

• binary

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

• mappable

  Checks whether the filehandle/layer is memory mappable. It is the same as binary, except that the utf8 layer is accepted.

• buffered

  Check whether the filehandle/layer is buffered.

• readable

  Check whether the filehandle/layer is readable.

• writeable

  Check whether the filehandle/layer is writeable.

• open

  Check whether the filehandle/layer is open.

• temp

  Check whether the filehandle/layer refers to a temporary file.

• can_crlf

  Checks whether layer $argument (or any layer if $argument it not given) can do crlf translation.

• line_buffered

  Check whether the filehandle is in line-buffering mode.

• autoflush

  Checks wheter the filehandle is in unbuffering mode. Note that this is not the opposite of buffering, but more similar to autoflush, hence the name of this test.

• buffer_size

  Check whether the buffer size is equal to $argument.

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

get_buffer_sizes($fh)

Returns a list of buffer sizes for all buffered layers. Unbuffered layers are skipped.

AUTHOR

Leon Timmermans <fawaka@gmail.com>

COPYRIGHT AND LICENSE

This software is copyright (c) 2010 by Leon Timmermans.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.