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Return Values: Functions Return Data

Functions return exit codes. Or output. Use both.

Here's the thing: Functions return exit codes. Or you can capture output. Use what fits.

Exit Codes​

function check_file() {
    if [ -f "$1" ]; then
        return 0
    else
        return 1
    fi
}

check_file "test.txt"
if [ $? -eq 0 ]; then
    echo "File exists"
fi

My take: Exit codes are 0 for success, non-zero for failure. Use them.

Capturing Output​

function get_name() {
    echo "John"
}

name=$(get_name)
echo "$name"

My take: Capture output with $(). Use it for data.

Both​

function process() {
    if [ $# -eq 0 ]; then
        return 1
    fi
    echo "Processed: $1"
    return 0
}

result=$(process "data")
if [ $? -eq 0 ]; then
    echo "$result"
fi

My take: Use both. Exit code for success. Output for data.

Common Patterns​

Return Status​

function validate() {
    if [ -z "$1" ]; then
        return 1
    fi
    return 0
}

Return Data​

function get_config() {
    echo "/etc/myapp.conf"
}

config=$(get_config)

What's Next?​

Now that you understand return values, let's talk about Local Variables.

Personal note: Return values confused me at first. Then I learned: exit codes for status, output for data. Now I use both. They're useful. Learn them.