As the editor at the Linux Gazette, I get a lot of articles, code, etc. that's been written in every possible variety of editor out there and sometimes contains weird and invisible characters. My solution was to code up a script that I called "weirdchar" that will display and highlight the characters and their ASCII values along with the line (and line number) where they occur. It's solved and prevented a huge variety of problems for me over the years.

Note: this is *nix-specific (works in Linux and Solaris), since it uses an external prog.

#!/usr/bin/perl -w
# Created by Ben Okopnik on Tue Feb 15 18:48:24 EST 2005
# Weird character highlighter

my $a=`/usr/bin/tput -T $ENV{TERM} smso`; # Start 'standout' mode
my $b=`/usr/bin/tput -T $ENV{TERM} rmso`; # End 'standout' mode
my $re = qr/([^\011\012\015\040-\176])/;  # "Inverted" list of valid c
+hars

while (<>){
    print "Line $.: $_" if s/$re/"$a\\" . sprintf( "%03o", ord $1 ) . 
+$b/eg;
}
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-- 
Human history becomes more and more a race between education and catastrophe. -- HG Wells