This program is a wrapper for latexmk. I want latexmk to be quiet
on success, and to be terse on failure. texfot isn't quiet enough,
-silent is too quiet, &c.

You need

 o lua-spawn [ https://github.com/daurnimator/lua-spawn ]
 o lunix     [ http://25thandclement.com/~william/projects/lunix.html ]
 o lpeg      [ http://www.inf.puc-rio.br/~roberto/lpeg/ ]

Invoke it as

    latexmk-quiet /path/to/latexmk [ args to latexmk ]

Configure it by editing the file to add more lines to scan for. If
you don't use a setup that exactly mirrors mine, it will probably
eat lines you don't want eaten.

See Makefile.example for a Makefile that I use(d at one point)
involving latexmk-quiet.