One way using \D: 
use warnings;
use strict;

while (<DATA>) {
    chomp;
    print "This is an invalid entry: $_\n" if /\D/;
}

__DATA__
555
3
1234
11-55
fadf
000
-402
1 2
1.2

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In reply to Re: using int and the range function by toolic
in thread using int and the range function by Melderon

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