functions.md

Functions

Syntax

function fn[()]
[function] fn()

Example

function get_name() {
	echo 'Mark'
}

$ echo "You are $(get_name)"
> You are Mark

Arguments

function trim() {
	text="$1"
	length="$2"

	echo ${text:0:length}
}

$ trim 'hello world' 5
> hello

variable	value
$1	first argument
$#	number of arguments
$*	all arguments
$@	all arguments

$* vs. $@

• when not double-quoted, $* and $@ are the same (expand to separate strings)
• when double-quoted, "$*" expands to a single string separated by space ("$1 $2 $n")
• when double-quoted, "$@" expands to separate strings ("$1" "$2" "$n")

function allArgsTogether() {
	for w in "$*"; do
		echo --${w}--
	done
}

$ allArgsTogether abc def
> --abc def--

function allArgsAlone() {
	for w in "$@"; do
		echo --${w}--
	done
}

$ allArgsAlone abc def
> --abc--
> --def--

Scope

fn() {
	a=1
	local b=2

	echo $a
	echo $b
}

$ echo $a
>
$echo $b
>

$ fn
> 1
> 2

echo $a
> 1
echo $b
>

Shifting Arguments

fn() {
	echo "$1 $2 $3"
	shift
	echo "$1 $2 $3"
	shift
	echo "$1 $2 $3"
	shift
	echo "$1 $2 $3"
}

$ fn A B C
> A B C
> B C
> C
>

sum() {
	let s=0

	until [ -z $1 ]; do
		(( s += $1 ))
		shift
	done

	echo $s
}

$ sum 1 2 3 4
> 10

Returning Values

Bash functions don't allow returning a value.

• they can give a value by echo-ing it:

getFive() {
	local five=5
	echo $five
}

$ getFive
> 5

$ result="$(getFive)"
$ echo $result
> 5

• or by setting a global variable:

getFive() {
	five=5
}

$ getFive
$ echo $five
> 5

The return keyword

The return keyword is not thought to return a value from function. Its task is terminating the function. A numeric value can be used along with return to state "exit status" of the function (something like in exit statement). The status can be accessed from the $? variable.

getAB() {
	echo A
	echo B
	return
	echo C
}

$ getAB
> A
> B

greet() {
	echo hello
	return 120
}

$ echo $?
> 0

$ greet
> hello

$ echo $?
> 120

$ echo $?
> 0

Raising Errors

funktion() {
	# non-zero status
	return 1
}

if funktion; then
	echo 'success'
else
	echo 'failure'
fi

> failure