delete 1st line in text file

Since it's just the first line:

#!/usr/bin/perl -w
use strict;

my $file = $ARGV[0] or die "Please include the filename.\n";

my $contents;
open (ORG, "$file") or die "Can't open $file: $!\n";
$_ = <ORG>;
{ local $/; $contents = <ORG>; }
open (OUT, ">$file") or die "Can't open new $file: $!\n";
print OUT $contents;

If you'd prefer to get a bit more verbose, this will take the input and the output filenames on the command line, giving you a couple of attempts to get both right, avoid overwriting existing files, etc.

#!/usr/bin/perl -w
use strict;
$| = 1;

if (@ARGV != 2) {
    my ($script) = ($0 =~ /[\/|\\]?([\w\.]+)$/);
    print "Usage: $script org_file new_file\n";
    exit;
}

unless (-e $ARGV[0]) {
    my $file;
    print "\nNo file named $ARGV[0] found.  Retry (y/n) [n]? ";

    my $ans = <STDIN>;
   
    if ($ans =~ /^y(es)?\n$/i) {
        print "\nEnter new filename: ";
        $file = <STDIN>;
        chomp ($file);
        if (($file) && (-e $file)) {
            $ARGV[0] = $file;
        } else {
            print "\nCan't find second attempt at file to alter.\n";
            print "\nQuitting. No changes made.\n";
            exit;
        }
    } else {
        print "\nQuitting. No changes made.\n";
        exit;
    }
}

if (-e $ARGV[1]) {
    print "\nA file named $ARGV[1] already exists and will be overwritten.  Re-enter output file name (y/n) [n]? ";

    my $ans = <STDIN>;
   
    if ($ans !~ /^y(es)?\n$/i) {
        print "\n$ARGV[1] will be overwritten.  Are you sure? (y/n) [n]? ";
        my $ans = <STDIN>;
        if ($ans !~ /^y(es)?\n$/i) {
            print "\nQuitting. No changes made.\n";
            exit;
        }
    } else {
        print "\nEnter new filename: ";
        my $new_outfile = <STDIN>;
        chomp ($new_outfile);
        if ($new_outfile) {
            if (-e $new_outfile) {
                print "\nA file named $new_outfile already exists and will be overwritten.  Continue (y/n) [n]? ";
                my $ans = <STDIN>;
                if ($ans !~ /^y(es)?\n$/i) {
                    print "\nQuitting. No changes made.\n";
                    exit;
                }
            }
            $ARGV[1] = $new_outfile;
        } else {
            print "\nQuitting. No changes made.\n";
            exit;
        }
    }
}

my $contents;
open (ORG, "$ARGV[0]") or die "Can't open $ARGV[0]: $!\n";
$_ = <ORG>;
{ local $/; $contents = <ORG>; }
open (OUT, ">$ARGV[1]") or die "Can't open $ARGV[1]: $!\n";
print OUT $contents;

print "\nDone.\n";