OK, now that's fixed, try this:

use Modern::Perl;
use autodie;

my $infile  = '/Users/ts/desktop/work/numbers.txt'; # Hmm...
my $outfile = 'Users/ts/full_number.txt';           # leading '/' or n
+ot?

open my $in, '<', $infile;

my @result;
while ( <$in> ) {
    my ( $index, $value ) = split;
    $result[$index] = $value;
}

close $in;

open my $out, '>', $outfile;
say $out "$_\t", $result[$_] || 0 for 1 .. 3_000_050;
close $out;
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Hi i tried doing this but i can't seem to open the output file to write in it i checked and it is definatly the right path the same happened with the previous attempt where the results just came up on terminal and not the outputfile i tried ending with a / but no difference

Can't open 'Users/ts/full_number.txt/' for writing: 'No such file or directory' at ./program13.txt line 18

EDIT OH i understand now leading /!! yes that fixed it thank you very much

Sorry, I should have used the built-in stuff. Modern::Perl basically saves a few lines of typing by activating some things that are good practices for every program.