Technotes for future me

Bash functions

Declaring Functions

Note: the () after the function name is optional.

my_func() {
    printf "Hello!\n"

# Call it with

Passing Parameters

Note: Bash doesn’t support prototyping, parameter types or references.

my_func() {
    printf "Hello %s %s\n" "$1" "$2"

my_func "literal 1" "$var2"

It is good style to “shift” parameters like this

my_func() {
    param1=$1; shift
    param2=$1; shift

    printf "Hello %s %s\n" "$param1" "$param2"

Return Values

You can return numbers only! Similar to program exit codes, function have return codes. Check below to see how to return data from a function.

my_func() {
    return 1


# Check return code
if [ $? -ne 0 ]; then
    printf "Return code: %d\n" $?

Returning data from a function

The best way to return data is catching the functions STDOUT using $()

my_func() {
    printf "Some output lines\nLine2\nLine3\n"

Last updated on 31 Jan 2021
Published on 25 Dec 2019
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