Use ((...)) for arithmetic tests and [[...]] for other tests. [...] is for POSIX compatibility and not as useful as [[...]] though I don't remember the specifics.

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jonhohle 5 hours ago | parent [-]

[[…]] is a bash (probably other shells, too) built in. […] could be a built in, or could be a symlink to /bin/test.

	▲	jcynix 4 hours ago \| parent [-]
		The [[…]] version was introduced in Peter Korn's korn shell, ksh88 IIRC.