in reply to Extracting Image/File Metadata

You can use sysread to read the header out of the file. Then, use something like Data::FixedFormat or Parse::FixedLength to decode the information. These modules use pack and unpack to manipulate buffers of (possibly binary) data. 

---
print map { my ($m)=1<<hex($_)&11?' ':'';
$m.=substr('AHJPacehklnorstu',hex($_),1) }
split //,'2fde0abe76c36c914586c';

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Re: Re: Extracting Image/File Metadata
by JunkGuy (Initiate) on Feb 05, 2003 at 23:47 UTC
    I think sysread will work for me, except for one thing: I need to be able to pull out and retain some data in binary format. I know that pack adn unpack is used for that, as you stated, but I can't seem to get it to work. Is there any special trick to using sysread with pack and unpack? Thanks for your time and your reply.
[reply]

      I use the code below to get some informatiion out of WAV files. Maybe it will help you read your files.

      #!/usr/bin/perl -w

use strict;
use Fcntl;
 
my $fnm = shift;
sysopen WAV,$fnm,O_RDONLY;
my $riff;
sysread WAV,$riff,12;
my $fmt;
sysread WAV,$fmt,24;
my $data;
sysread WAV,$data,8;
close WAV;

# RIFF header: 'RIFF', long length, type='WAVE'
my ($r1,$r2,$r3) = unpack "A4VA4", $riff;
# WAV header, 'fmt ', long length, short unused, short channels,
# long samples/second, long bytes per second, short bytes per sample,
# short bits per sample
my ($f1,$f2,$f3,$f4,$f5,$f6,$f7,$f8) = unpack "A4VvvVVvv",$fmt;
# DATA header, 'DATA', long length
my ($d1,$d2) = unpack "A4V", $data;
print << "EOF";
RIFF header: $r1, length $r2, type $r3
 
Format: $f1, length $f2, always $f3, channels $f4,
        sample rate $f5, bytes per second $f6,
        bytes per sample $f7, bits per sample $f8
 
Data: $d1, length $d2
EOF

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      ---
print map { my ($m)=1<<hex($_)&11?' ':'';
$m.=substr('AHJPacehklnorstu',hex($_),1) }
split //,'2fde0abe76c36c914586c';

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