while(1)                             fish                             while(1)

       while - perform a command multiple times

       while CONDITION; COMMANDS...; end

       while repeatedly executes CONDITION, and if the exit status is 0, then
       executes COMMANDS.

       The exit status of the while loop is the exit status of the last
       iteration of the COMMANDS executed, or 0 if none were executed. (This
       matches other shells and is POSIX-compatible.)

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

       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.

Version 3.0.2                   Tue Mar 26 2019                       while(1)