Introduction Although most users think of the shell as an interactive
command interpreter, it is really a programming language in which each
statement runs a command. Because it must satisfy both the interactive
and programming aspects of command execution, it is a strange language,
shaped as much by history as by design. Brian Kernighan and Rob Pike,
The UNIX Programming Environment, Prentice-Hall, 1984 The shell is a
programming language. Don't let anyone tell you otherwise. The shell is
not just glue that sticks bits together. The shell is a lot more than a
tool that runs other tools. The shell is a complete programming
language! When a Linux user asked me about membership databases, I asked
him what he really needed. He wanted to store names and addresses for a
couple of hundred members and print mailing labels for each of them. I
recommended using a text editor to store the information in a text file,
and I provided a shell script to create the labels in PostScript. (The
script, ps-labels, appeared in my first book, Shell Scripting Recipes: A
Problem-Solution Approach. ) When the SWEN worm was dumping hundreds of
megabytes of junk into my mailbox every few minutes, I wrote a shell
script to filter them out on the mail server and download the remaining
mail to my home computer. That script has been doing its job for several
years.
