You probably want to read the header, then unpack the data based on that, it might be 8 bit or 16 bit, mono or stereo, etc. Here is a way to read the header and determine it's playlength based on byte size, number of channels, etc.

#!/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;

my $playlength = $d2/$f6;

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
Playlength: $playlength seconds
EOF
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