#!/usr/bin/perl
# chist.perl -- print histogram of byte values
# (useful for seeing if text contains invisible characters)

while (<>)
{
   @chars = split //;
   for $c ( split // ) {
     $chist[ord($c)]++;
   }
}
for ( $i=0; $i<256; $i++ ) {
   printf("%d\tx%0.2x\n", $chist[$i], $i) if ( $chist[$i] );
}
# there are ways to reduce that to a fairly short one-liner,
# but you may want to add options...