I agree with much of this. However, i think it should be: 
$seed = $tab[0];

[download]
Etbr77, here is my version (which is nearly identical to AnonMonk's): 
use warnings;
use strict;

open TAB, '<', 'test.txt' or die "Can not open file: $!";
my $seed = 1.04;
while (<TAB>) {
    chomp;
    my @tab = split / /;
    my $diff = $tab[0] - $seed;
    if ($diff >= 0.1) {
        print "tab[0]=$tab[0]\n";
        $seed = $tab[0];
    } 
}
close TAB;

[download]
Since I really have no idea what your input file looks like, I created my own sample input file (test.txt): 
3
5 6 7
2 22 222
10 9

[download]
When I run this script, I get the following output: 
tab[0]=3
tab[0]=5
tab[0]=10

[download]
If this is not what you are looking for, please provide a small sample of your input, and expected output.

Update: Removed unnecessary else, thanks to Eimi Metamorphoumai.

In reply to Re^2: Simple iteration problem by toolic
in thread Simple iteration problem by Etbr77

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