true and false

true and false do nothing at all. Their only product is an exit status: true always succeeds, false always fails.

true
false

$ true ; echo $?
0
$ false ; echo $?
1

true exits 0. false exits 1. They take no arguments that matter, produce no output, and have no effect on anything.

What they are for #

A command that is only an exit status is useful as a fixed value in places that expect a command:

• An always-true or always-false loop. while true is the standard way to write a loop that runs until something inside it breaks out.
• A deliberate placeholder. Setting a configurable command to true makes that step do nothing and "succeed"; false makes it a step that always fails.
• A known result in a test. When a script or a condition needs a guaranteed pass or fail to check against, true and false provide it.

They are the simplest commands there are — and the overview's note on exit status is the whole idea behind them.

Exit status #

Each command also accepts --help and --version; using one of those makes the command print that text instead of doing its usual nothing. (A write error while printing causes even true to exit non-zero.)