The test command is used in shell commands to test various conditions. This is most useful in shell scripts.
Most shells provide this as a builtin, but this is also present in the GNU Coreutils as a utility. The two forms may have different behavior. Most (all?) Linux distributions incorporate the utility from the GNU Coreutils: man page
- false - gives exit status 1.
- true - gives exit status 0.
- expr - evaluates an expression, result to stdout