UNIX for Beginners Questions & Answers

#!/bin/bash
preprocess() {
  tr -d '[[:punct:][:digit:]@]' \
    | tr '[[:space:]]' '\n' \
    | grep -v '^\(.\)\1*$'
}

paste <(preprocess <"$1") <(preprocess <"$1" | rev) \
  | awk '$1 == $2 && (length($1) >= 3) { print $1 }' \
  | sort | uniq -c

chmod +x palindrome

aaa aia xyzzyx xxxxxx naan shahs palindromes
aaa aia xyzzyx xxyxxyxx naan shahs toot

./palindrome file

   2 aia
   2 naan
   2 shahs
   1 toot
   1 xxyxxyxx
   2 xyzzyx

$ ksh palindrome file
   2 aia
   2 naan
   2 shahs
   1 toot
   1 xxyxxyxx
   2 xyzzyx
$