Wicked Cool Shell Scripts

#12 Building a Shell Script Library

Many of the scripts in this chapter have been written as functions rather than as stand-alone scripts so that they can be easily and gracefully incorporated into other scripts without incurring the overhead of making system calls. While there's no #include feature in a shell script, as there is in C, there is a tremendously important capability called sourcing a file that serves the same purpose.

To see why this is important, let's consider the alternative. If you invoke a shell script within a shell, by default that script is run within its own subshell. You can immediately prove this experimentally:

$ cat tinyscript.sh
test=2
$ test=1
$ tinyscript.sh
$ echo $test
1

Because this script changed the value ...