fifolog

when run as fifolog PREFIX fifolog reads '\n' delimited lines from stdin, then outputs lines in the format:

PREFIX || LINE[0..MIN(LEN(LINE) - 1, PIPE_BUF - LEN(PREFIX) - 1)] || '\n'

If PREFIX is longer than 510 characters it is truncated to 510 characters.

fifolog terminates with a non zero exit code if any IO errors are encountered.

This enables atomic labeled writes to a unix pipe. Consider the following example:

$ mkfifo logstream
$ (cat data1 | fifolog data-1: > logstream)  & \
  (cat data2 | fifolog data-2: > logstream)  & \
  (cat data3 | fifolog data-3: > logstream)  &
$ cat logstream
data-1:haha
data-2:hoho
data-3:hehe
...

The terminal will get interleaved (but not jumbled) labeled line output guaranteed because each labeled write to fifo is smaller than PIPE_BUF.