un pipe de six commandes shell et s'est plié

Dans le livre Classic Schell Scripting de chez O'reilly [»], il y a un exemple d'analyse fréquentielle des mots d'un texte pour montrer la puissance des pipes. En six commandes et c'est plié.

#! /bin/sh
# Read a text stream on standard input, and output a list of
# the n (default: 25) most frequently occurring words and
# their frequency counts, in order of descending counts, on
# standard output.
#
# Usage:
# wf [n]
tr -cs A-Za-z\' '\n' | # Replace nonletters with newlines
 tr A-Z a-z | # Map uppercase to lowercase
 sort | # Sort the words in ascending order
 uniq -c | # Eliminate duplicates, showing their counts
 sort -k1,1nr -k2 | # Sort by descending count, and then by ascending word
 sed ${1:-25}q # Print only the first n (default: 25) lines; see Chapter 3