A Unix novice came to Master Foo and said: “I am confused. Is it not the Unix way that every program should concentrate on one thing and do it well?”

Master Foo nodded.

The novice continued: “Isn't it also the Unix way that the wheel should not be reinvented?”

Master Foo nodded again.

“Why, then, are there several tools with similar capabilities in text processing: sed, awk and Perl? With which one can I best practice the Unix way?”

Master Foo asked the novice: “If you have a text file, what tool would you use to produce a copy with a few words in it replaced by strings of your choosing?”

The novice frowned and said: “Perl's regexps would be excessive for so simple a task. I do not know awk, and I have been writing sed scripts in the last few weeks. As I have some experience with sed, at the moment I would prefer it. But if the job only needed to be done once rather than repeatedly, a text editor would suffice.”

Master Foo nodded and replied: “When you are hungry, eat; when you are thirsty, drink; when you are tired, sleep.”

Upon hearing this, the novice was enlightened.