C. is continue to be interested in regular expression. The most fun one seems to be the way to find palindromes
find palindromes with 5 letters
cat $words | grep '(.)(.)(.)\2\1'
Find any word starting with C, replace with K
cat tck | sed 's/^C/K/'
Find any word ending in Y, replace with I
cat tck | sed 's/Y$/I/
find words with either 1-3 or 5-7
cat no.file | grep '[1-3]|5-7]'
find words with any letter between m and p
cat /usr/share/dict/words | grep '[m-p]'