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Parse::Binary::FixedFormat - Convert between fixed-length fields and hashes


   use Parse::Binary::FixedFormat;

   my $tarhdr =
      new Parse::Binary::FixedFormat [ qw(name:a100 mode:a8 uid:a8 gid:a8 size:a12
                                 mtime:a12 chksum:a8 typeflag:a1 linkname:a100
                                 magic:a6 version:a2 uname:a32 gname:a32
                                 devmajor:a8 devminor:a8 prefix:a155) ];
   my $buf;
   read TARFILE, $buf, 512;

   # create a hash from the buffer read from the file
   my $hdr = $tarhdr->unformat($buf);   # $hdr gets a hash ref

   # create a flat record from a hash reference
   my $buf = $tarhdr->format($hdr);     # $hdr is a hash ref

   # create a hash for a new record
   my $newrec = $tarhdr->blank();


Parse::Binary::FixedFormat can be used to convert between a buffer with fixed-length field definitions and a hash with named entries for each field. The perl pack and unpack functions are used to perform the conversions. Parse::Binary::FixedFormat builds the format string by concatenating the field descriptions and converts between the lists used by pack and unpack and a hash that can be reference by field name.


Parse::Binary::FixedFormat provides the following methods.


To create a converter, invoke the new method with a reference to a list of field specifications.

    my $cvt =
        new Parse::Binary::FixedFormat [ 'field-name:descriptor:count', ... ];

Field specifications contain the following information.


This is the name of the field and will be used as the hash index.


This describes the content and size of the field. All of the descriptors get strung together and passed to pack and unpack as part of the template argument. See perldoc -f pack for information on what can be specified here.

Don't use repeat counts in the descriptor except for string types ("a", "A", "h, "H", and "Z"). If you want to get an array out of the buffer, use the count argument.


This specifies a repeat count for the field. If specified as a non-zero value, this field's entry in the resultant hash will be an array reference instead of a scalar.


To convert a buffer of data into a hash, pass the buffer to the unformat method.

    $hashref = $cvt->unformat($buf);

Parse::Binary::FixedFormat applies the constructed format to the buffer with unpack and maps the returned list of elements to hash entries. Fields can now be accessed by name though the hash:

    print $hashref->{field-name};
    print $hashref->{array-field}[3];


To convert the hash back into a fixed-format buffer, pass the hash reference to the format method.

    $buf = $cvt->format($hashref);


To get a hash that can be used to create a new record, call the blank method.

    $newrec = $cvt->blank();


Each Parse::Binary::FixedFormat instance contains the following attributes.


Names contains a list of the field names for this variant.


Count contains a list of occurrence counts. This is used to indicate which fields contain arrays.


Format contains the template string for the Perl pack and unpack functions.


Audrey Tang <>

Based on Data::FixedFormat, written by Thomas Pfau <>


Copyright 2004-2009 by Audrey Tang <>.

Copyright (C) 2000,2002 Thomas Pfau. All rights reserved.

This module is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.