Hi Csonytii,

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

my $sum;
my $count;

open my $input, '<', 'meres.txt' or die "ERROR: $!\n";
while(my $line = <$input>) {                        # read line to $li
+ne
    chomp $line;                                    # remove eol
    if ($line =~ /(-?\d+)/) {                       # match to numbers
+ and optional leading minus, the match will be in $1
        #print($1."\n");
        $sum += $1;                                 # summing up
        $count++;                                   # count items
    }
}
close $input;
print 'Average: ', $sum/$count, "\n";
[download]

HTH

Update:Typo fixed.