test returns a status of 0 (true) or 1 (false) depending on the evaluation of the conditional expression expr. Each part of the expression must be a separate argument.
test has file status checks, string operators, and numeric comparison operators.
test has an alternate form that uses opening and closing square brackets instead a leading ‘test’. For example, instead of ‘test -d /’, you can write ‘[ -d / ]’. The square brackets must be separate arguments; for example, ‘[-d /]’ does not have the desired effect. Since ‘test expr’ and ‘[ expr ]’ have the same meaning, only the former form is discussed below.
test expression test [ expression ] [ ] [ option
Due to shell aliases and built-in test functions, using an
unadorned test interactively or in a script may get you
different functionality than that described here. Invoke it via
env test ...) to avoid interference
from the shell.
If expression is omitted, test returns false. If expression is a single argument, test returns false if the argument is null and true otherwise. The argument can be any string, including strings like ‘-d’, ‘-1’, ‘--’, ‘--help’, and ‘--version’ that most other programs would treat as options. To get help and version information, invoke the commands ‘[ --help’ and ‘[ --version’, without the usual closing brackets. See Common options.
0 if the expression is true, 1 if the expression is false, 2 if an error occurred.