while(1)

NAME
while -- perform a command multiple times

  Synopsis

while CONDITION; COMMANDS...; end

  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.

You can use and or or for complex conditions. Even more complex control can be achieved with while true containing a break.

  Example

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