Including/importing a library script and using external functions

To prepare for this example, create the following two files and open both:

• io_maker.sh
• library.sh

Inside library.sh, add the following:

#!/bin/bash

function create_file() {
    local FNAME=$1
    touch "${FNAME}"
    ls "${FNAME}" # If output doesn't return a value - file is missing
}

function delete_file() {
    local FNAME=$1
    rm "${FNAME}"
    ls "${FNAME}" # If output doesn't return a value - file is missing
}

Inside io_maker.sh, add the following:

#!/bin/bash

source library.sh # You may need to include the path as it is relative
FNAME="my_test_file.txt"
create_file "${FNAME}"
delete_file "${FNAME}"

exit 0

When you run the script, you should get the same output:

$ bash io_maker.sh
my_test_file.txt
ls: cannot access 'my_test_file.txt': No such file or directory

Although not obvious, we can see that both functions are executed. The first line of output is the ls command, successfully finding my_test_file.txt after creating the file in create_file(). In the second line, we can see that ls returns an error when we delete the file passed in as a parameter. 

Unfortunately, up until now, we have only been able to create and call functions, and execute commands. The next step, discussed in the next section, is to retrieve commands and function return codes or strings.