#!/usr/bin/perl

open( Z, "test.zip" );

sub error {
    print "The file is corrupt.\n";
    exit;
}

sub readstr {
    my $received;
    error() if eof Z;
    $received .= getc(Z) . " " for ( 1 .. $_[0] );
    return $received;
}

sub readint {
    my $received = 0;
    error() if eof Z;
    $received = $received * 255 + ord( getc(Z) ) for ( 1 .. $_[0] );
    return $received;
}

while ( !eof Z ) {
    my $head     = readstr(4);    # PK^C^D
    my $versions = readstr(4);
    # ...
    my $filenamelength = readint(2);
    # ...
    # Parse the rest of this file
    # Until we get an error or go on to the next file header
}

close(Z);