NAME

IO::ReadHandle::Chain - Chain several sources through a single file read handle

VERSION

Version 1.2.2

SYNOPSIS

    use IO::ReadHandle::Chain;

    open $ifh, '<', 'somefile.txt';
    $text = 'This is some text.';
    $cfh = IO::ReadHandle::Chain->new('file.txt', \$text, $ifh);
    print while <$cfh>;
    # prints lines from file 'file.txt', then lines from scalar $text,
    # then lines from file handle $ifh

    $line_number = $.; # cumulative line number from all sources

    @lines = <$cfh>;              # or get all lines at once

    # or read bytes instead
    $buffer = '';
    $bytecount = read($cfh, $buffer, 100);
    $bytecount = sysread($cfh, $buffer, 100);

    # or single characters
    $c = getc($cfh);

    close($cfh);

    # OO, too
    $line = $cfh->getline;
    @lines = $cfh->getlines;
    $bytecount = $cfh->read($buffer, $size, $offset);
    $bytecount = $cfh->sysread($buffer, $size, $offset);
    $c = $cfh->getc;
    $line_number = $cfh->input_line_number;
    $cfh->close;
    print "end!\n" if $cfh->eof;

    # specific to IO::ReadHandle::Chain:
    $current_source = $cfh->current_source;

    $cfh->set_field('mykey', $myvalue);
    $value = $cfh->get_field('mykey');
    $cfh->remove_field('mykey');

DESCRIPTION

This module chains any number of data sources (scalar, file, IO handle) together for reading through a single file read handle. This is convenient if you have multiple data sources of which some are very large and you need to pretend that they are all inside a single data source.

Use the IO::ReadHandle::Chain object for reading as you would any other filehandle.

The module raises an exception if you try to write or seek or tell through an IO::ReadHandle::Chain.

When reading by lines, then the input record separator $/ is used to separate the data into lines.

The chain filehandle object does not close any of the file handles that are passed to it as data sources.

An IO::ReadHandle::Chain provides some methods that are not available from a standard IO::Handle:

The "set_field", "get_field", and "remove_field" methods manipulate fields in a private area of the object -- private in the sense that the other methods of the module do not access that area; It's all yours.

The "current_source" method identifies the current source being read from.

METHODS

new

  $cfh = IO::ReadHandle::Chain->new(@sources);

Creates a filehandle object based on the specified @sources. The sources are read in the order in which they are specified. To read from a particular file, specify that file's path as a source. To read the contents of a scalar, specify a reference to that scalar as a source. To read from an already open file handle, specify that file handle as a source.

Croaks if any of the sources are not a scalar, a scalar reference, or a file handle.

close

  $cfh->close;
  close $cfh;

Closes the stream. Closes any filehandles that the instance created, but does not close any filehandles that were passed into the instance as sources.

Returns the object.

current_source

  $current_source = $cfh->current_source;

Returns text describing the source that the next input from the stream will come from, or (at the end of the data) that the last input came from.

For a source specified as a path name, returns that path name.

For a source specified as a filehandle, returns the result of calling the current_source method on that filehandle, unless it returns the undefined value or the filehandle doesn't support the current_source method, in which case the current method returns the stringified version of the filehandle.

For a source specified as a reference to a scalar, returns SCALAR(...) with the ... replaced with up to the first 10 characters of the scalar, with newlines replaced by spaces.

eof

  $end_of_data = eof $cfh;
  $end_of_data = $cfh->eof;

Returns 1 when there is no (more) data to read from the stream, and '' otherwise.

get_field

  $value = $cfh->get_field($field);
  $value = $cfh->get_field($field, $default);

Returns the value of the private field $field from the filehandle.

If that field does not yet exist, and if $default is not specified, then does not modify the object and returns the undefined value.

If the field does not yet exist but $default is specified, then creates the field, assigns it the value $default, and then returns that value.

getc

  $char = $cfh->getc;
  $char = getc $ifh;

Returns the next character from the stream, or undef if there are no more characters.

getline

  $line = $cfh->getline;
  $line = <$cfh>;
  $line = readline $cfh;

Reads the next line from the stream. The input record separator ($/) or end-of-data mark the end of the line.

getlines

  @lines = $cfh->getlines;
  @lines = <$cfh>;

Reads all remaining lines from the stream. The input record separator ($/) or end-of-data mark the end of each line.

input_line_number

  $line_number = $cfh->input_line_number;                # get
  $previous_value = $cfh->input_line_number($new_value); # set
  $line_number = $.;     # until next read from any filehandle

Returns the number of lines read through the filehandle, and makes that number also available in the special variable $.. If no lines have been read yet, then returns the undefined value.

The line number is cumulative across all sources specified for the IO::ReadHandle::Chain.

If an argument is specified, then the method sets the current line number to that value -- without changing the position in the stream.

open

  $cfh->open(@sources);

(Re)opens the IO::ReadHandle::Chain object, for reading the specified @sources. See "new" for details about the @sources. Croaks if any of the sources are unacceptable.

Returns the IO::ReadHandle::Chain on success.

read

  $cfh->read($buffer, $length, $offset);
  read $cfh, $buffer, $length, $offset;

Reads up to $length characters from the stream into the $buffer at offset $offset. Returns the number of characters read, or 0 when there are no more characters.

remove_field

  $cfh->remove_field($field);

Removes the filehandle's private field with the specified name, if it exists. Returns the filehandle.

set_field

  $cfh->set_field($field, $value);

Sets the filehandle's private field with key $field to the specified $value. Returns the filehandle.

AUTHOR

Louis Strous, <lstrous at cpan.org>

BUGS

Please report any bugs or feature requests to bug-io-readhandle-chain at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=IO-ReadHandle-Chain. 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 IO::ReadHandle::Chain

You can also look for information at:

LICENSE AND COPYRIGHT

Copyright 2017, 2018 Louis Strous.

This program is free software; you can redistribute it and/or modify it under the terms of the the Artistic License (2.0). You may obtain a copy of the full license at:

http://www.perlfoundation.org/artistic_license_2_0

Any use, modification, and distribution of the Standard or Modified Versions is governed by this Artistic License. By using, modifying or distributing the Package, you accept this license. Do not use, modify, or distribute the Package, if you do not accept this license.

If your Modified Version has been derived from a Modified Version made by someone other than you, you are nevertheless required to ensure that your Modified Version complies with the requirements of this license.

This license does not grant you the right to use any trademark, service mark, tradename, or logo of the Copyright Holder.

This license includes the non-exclusive, worldwide, free-of-charge patent license to make, have made, use, offer to sell, sell, import and otherwise transfer the Package with respect to any patent claims licensable by the Copyright Holder that are necessarily infringed by the Package. If you institute patent litigation (including a cross-claim or counterclaim) against any party alleging that the Package constitutes direct or contributory patent infringement, then this Artistic License to you shall terminate on the date that such litigation is filed.

Disclaimer of Warranty: THE PACKAGE IS PROVIDED BY THE COPYRIGHT HOLDER AND CONTRIBUTORS "AS IS' AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES. THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT ARE DISCLAIMED TO THE EXTENT PERMITTED BY YOUR LOCAL LAW. UNLESS REQUIRED BY LAW, NO COPYRIGHT HOLDER OR CONTRIBUTOR WILL BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING IN ANY WAY OUT OF THE USE OF THE PACKAGE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

SEE ALSO

IO::ReadHandle::Include.