Supplementary to Abigail-II's advice here's example code of how you might insert a line into the beginning of a file using Tie::File

use strict;
use Tie::File;

tie(my @fl, 'Tie::File', 'somefile.txt') or die("ack - $!");
unshift @fl, 'a line of text here';
untie @fl;
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If you're not doing line-based insertion into your file then your best choice is to open a new file and write to that.
HTH

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broquaint