Hello roperl,

CPAN has the module Test::PureASCII, but it’s designed to function in a testing environment:

use strict;
use warnings;
use Test::PureASCII tests => 2;

for my $file ('ascii.txt', 'umlaut.txt')
{
    file_is_pure_ascii($file, "Only ASCII in $file");
}
[download]

Output (with suitable input files in the current directory):

17:00 >perl 1823_SoPW.pl
1..2
ok 1 - Only ASCII in ascii.txt
not ok 2 - Only ASCII in umlaut.txt
#   Failed test 'Only ASCII in umlaut.txt'
#   at 1823_SoPW.pl line 38.
#   non ASCII character sequence 0xc3, 0xb6 at line 5 in umlaut.txt
# Looks like you failed 1 test of 2.

17:00 >
[download]

Hope that’s of interest,