The `forx` program

forx runs a loop.

Interface

In an execlineb script:

     forx [ -p | -o okcodes | -x breakcodes ] variable { args... } loop...

forx reads a block and unquotes it. That block contains a list of args.
For each argument x in args..., forx runs loop as a child process, with variable=x added to its environment.
forx then exits 0.

-p : run in parallel. Do not wait for an instance of loop... to exit before spawning the next one. forx will still wait for all instances of loop to terminate before exiting, though.
-o okcodes : okcodes must be a comma-separated list of exit codes. If the -p flag hasn't been given and loop exits with one of the codes in okcodes, forx will run the following instances of the loop, but if the exit code is not listed in okcodes, forx will exit immediately with an approximation of the same exit code.
-x breakcodes : like the previous option, but with inverted meaning - the listed exit codes are codes that will make forx break the loop and exit, and the unlisted exit codes will make it keep looping.

You can start loop with "import -u variable" if you want variable substitution.