Regular Expressions
•awk – Aho, Alfred V.; Weinberger, Peter J.; and Kernighan Brian W. (1977)
https://en.wikipedia.org/wiki/AWK#Versions_and_implementations
http://linuxmeister.net/Commands/awk-example.html      http://linuxmeister.net/Notes/tabs-convert-to-spaces.html
•sed – stream editor (also used with Perl)
http://linuxmeister.net/Notes/using-sed-to-count-executable-files.html 
ls `env | grep PATH | grep -v XNLSPATH | sed -e 's/^PATH=//' | sed -e 's/\:/ /g'`  2>/dev/null  | wc -l
•grep – global regular expression search
http://linuxmeister.net/Notes/using-find-grep-xargs.html    http://linuxmeister.net/Commands/use-of-grep.html
find . -type f -name *.html | xargs grep johnmeister.com/linux | perl -pi -e 's$http://johnmeister.com/linux$http://linuxmeister.net$g'