#!/usr/bin/perl -w
use strict;
#deletes first numbytes of a file

use constant BLOCKSIZE => 128*1024;

die "Usage: $0 numbytes file [file ...]\n" if @ARGV < 2;

my $trunc_bytes = shift @ARGV;
my $files_done = 0;

for(@ARGV) {
    my $fh;
    unless(open $fh, "+<", $_) {
        warn "Couldn't open $_: $!\n";
        next;
    }
    my $filesize = -s $fh;
    while($filesize > $trunc_bytes + tell $fh) {
        seek $fh, $trunc_bytes, 1;
        my $bytes_read = read($fh, my $buffer, BLOCKSIZE);
        seek $fh, -$bytes_read -$trunc_bytes, 1;
        print $fh $buffer;
    }
    truncate $fh, tell $fh;
    close $fh;
    $files_done++;
}

exit ($files_done == 0);