#!/bin/bash
#
# Prefixes all lines on stdout and stderr with the process name (as determined by
# the SUPERVISOR_PROCESS_NAME env var, which is automatically set by Supervisor).
#
# Usage:
#   prefix-log command [args...]
#

# '-W interactive' is a `mawk` extension which disables buffering on stdout and sets line-buffered reads on
# stdin. The effect is that the output is flushed after each line, rather than being batched, which helps reduce
# confusion due to to interleaving of the different processes.
prefixer() {
    mawk -W interactive '{printf("%s | %s\n", ENVIRON["SUPERVISOR_PROCESS_NAME"], $0); fflush() }'
}
exec 1> >(prefixer)
exec 2> >(prefixer >&2)
exec "$@"