Check out Tie::File, it is part of the core module set. It will allow you to treat a file as an array of lines.

use Tie::File;

tie @array, 'Tie::File', filename or die ...;

# These are just like regular push, pop, unshift, shift, and splice
# Except that they modify the file in the way you would expect

push @array, new recs...;
my $r1 = pop @array;
unshift @array, new recs...;
my $r2 = shift @array;
@old_recs = splice @array, 3, 7, new recs...;

untie @array;            # all finished
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#!/usr/bin/perl -w
    use Tie::File;
    use strict;
    use warnings;
    
    tie my @in_lines, 'Tie::File', "infile";
    tie my @out_lines,'Tie::File', "outfile";
    
    my  $lines_to_transfer = 3;
    push @out_lines, splice @in_lines, 0,$lines_to_transfer;
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# Args are N, Oldfile, Newfile
# Get N and Newfile, leave Oldfile
my ($n, $newfile) = (shift,pop);
# Process inplace
$^I=1;
open(NEW, '>', $newfile) or die "$!: $newfile\n";
while (<>) {
  # Print first N lines to NEW
  if (1..$.==$n) { print NEW }
  # Everything else overwrites Oldfile
  else { print }
}
close NEW;
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You can not add/delete data from a file (all you can do is overwrite bytes).

So if you want to delete from the original file, then you have to re-write it...

Update: Great, getting downvoted. Thank you. All I was trying to do was trying to explain that in order to modify the file the file should be re-writed. which is exactly what Tie::File does! I'll guess I should stop posting.

use strict;

my $lines   = 10;
my $file_r  = "from_filename";
my $file_w  = "to_filename";
my (@_1, @_2);

open FH, $file_r or die $!;

$. > $lines and push @_1, $_ or push @_2, $_ while <FH>;

close FH;

open FH1, "> $file_r" or die $!;
open FH2, "> $file_w" or die $!;

print FH1 $_ for @_1;
print FH2 $_ for @_2;
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