[lang-ref] Null coalescing ( bash )

@test "null coalescing" {
	# x="${a:-not set}"
	# Use default if unset or empty.

	unset a
	x="${a:-not set}"
	[ "$x" == "not set" ]

	a=""
	x="${a:-not set}"
	[ "$x" == "not set" ]

	a="test"
	x="${a:-not set}"
	[ "$x" = "test" ]
}

@test "null coalescing alternative 1" {
	# x="${a-not set}"
	# Use default only if unset (empty counts as set).

	unset a
	x="${a-not set}"

	[ "$x" == "not set" ]

	a=""
	x="${a-not set}"
	[ "$x" == "" ]

	a="test"
	x="${a-not set}"
	[ "$x" = "test" ]
}

@test "null coalescing alternative 2" {
	# : "${x:=not set}"
	# If unset or empty, assign default to x (and expand to that value).
	# this is used for initialize value

	unset x
	: "${x:=not set}"
	[ "$x" = "not set" ]

	x=""
	: "${x:=not set}"
	[ "$x" = "not set" ]

	x="test"
	: "${x:=not set}"
	[ "$x" = "test" ]
}