A library for shell scripts

  Last modified on Sunday 12 July 2015

Programming languages like Python can make use of libraries of code to add ready-to-go capabilities to programs. Shell scripts don't use libraries but I learned this week it is possible to source a file in a shell script and add functions to the script as if they were entered directly (vs spawning a subshell). Very useful in creating your own library equivalent for the shell!

There are several functions I have created in previous scripts that are self-contained in their logic and can be re-used over and over again. This function - for example - adds a test whether or not the user executing a script has root privileges:

testRoot() {
local message="$scriptName requires ROOT privileges to do its job."
if [[ $UID -ne 0 ]]
    echo -e "\n$message"
    exit 1

I gathered up several other functions like this and created a Library.sh script that I place in my PATH. When I create a new shell script and want to access this library of functions I source it by adding:

. Library.sh

... and its contents are now available for inclusion in every script that needs it. Write once and use everywhere.

Sourcing a library file for the shell reminds me of HTML templates and CSS stylesheets for websites. Adding new functions or making improvements to existing ones in a single location means the changes ripple across every script that calls upon that location.

Source: Library.sh

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