\section while while - perform a command multiple times

\subsection while-synopsis Synopsis
\fish{synopsis}
while CONDITION; COMMANDS...; end
\endfish

\subsection while-description Description
`while` repeatedly executes `CONDITION`, and if the exit status
is 0, then executes `COMMANDS`.

If the exit status of `CONDITION` is non-zero on the first iteration,
`COMMANDS` will not be executed at all.

Use <a href="#begin">`begin; ...; end`</a> for complex conditions; more
complex control can be achieved with `while true` containing a
<a href="#break">break</a>.

\subsection while-example Example

`while test -f foo.txt; echo file exists; sleep 10; end`
outputs 'file exists' at 10 second intervals as long as
the file foo.txt exists.