in reply to file writing permission

You might also consider showing us the section of code that isn't writing the file. Are you checking the return values of the file I/O functions? eg:
open $fh, '>', "/tmp/blah" or die "File Open Problem: $!";

You could always have the or write to a log file somewhere that you are positive the web server has write access to (which is likely to be /tmp on most *nix machines). Also, I don't know what the script is for, but if it is a CGI that returns to the user, you could always debug by adding the following to the beginning of the script:

use CGI::Carp qw(fatalsToBrowser);

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Re^2: file writing permission
by Corion (Patriarch) on Nov 24, 2006 at 07:17 UTC
    open $fh, '>', "/tmp/blah" or die "File Open Problem: $!";

    Whenever you die because of some error, always include both, the reason and the filename! This makes the error diagnosis and remedy much much faster in my experience:

    open $fh, '>', "/tmp/blah" or die "File Open Problem with '/tmp/blah': + $!";