Linux source command (shell function library) [Basic Guide]

The source command is used to read a library file with various functions to the shell in a script file or the command prompt. It searches for library files located in the DIRECTORIES of the PATH variable or a specific file.

Examples:

$ source funcoes.sh $ source /caminho/ate/diretório/funcoes.sh arg1 arg2

In the example below, we will create a file called minhabiblioteca.sh with the following content:

#! /bin/bash

eh_o_root () {
[$ (id -u) -eq 0] && return $TRUE || return $FALSE
}

This file contains a function called “eh_o_root” that returns true if the logged-in user’s uid equals zero (root) or false when it returns another value.

Now let’s create a script called meuscript.sh that will use minhabiblioteca.sh as a function source:

#! /bin/bash 
# Let's read the minhabiblioteca.sh with the command 
source minhabiblioteca.sh 
eh_o_root && echo “You're the Root.” || echo “You're an ordinary user.” 

Now let’s change the permission of meuscript.sh to executable:

$ chmod +x meuscript.sh

When running meuscript.sh:

$. /meuscript.sh 
You are an ordinary user. 

The source command is very useful for reading a library of functions or variables that can be used by various scripts from shell.

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Uirá Endy Ribeiro

Uirá Endy Ribeiro is a Software Developer and Cloud Computing Architect with a 23-year career. He has master's degrees in computer science and fifteen IT certifications and is the author of 11 books recognized in the IT world market. He is also Director at Universidade Salgado de Oliveira and Director of the Linux Professional Institute - LPI Director's Board.