these are the two common ways (-s is more idiomatic).

it seems that you do not use strict;. i suggest you to put it together with use warnings; at the top of your script.

if $size is blank, an error has occured. you can check this by using this for example: 
my $filename = "test.pl";
my $size = -s $filename;
unless ($size) {
    die "error getting file size [$filename]: [$!]";
}

[download]
then check the error and correct it.

a common error seems to be the permission issue because the cgi script is executed using another user OR you are ín the wrong path (if relative). HTH

In reply to Re: Getting file size by kabel
in thread Getting file size by Willman023

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