#!/bin/sh

# Example of duplicating STDOUT+STDERR into a log file
# Copyright (C) 2016 Assaf Gordon <assafgordon@gmail.com>
# License: MIT
#
# This script demonstate how to setup logging of all STDOUT and STDERR
# outputs into log files (in addition to also outputing it to the
# original STDOUT/STDERR (e.g. the terminal).
#
# The function 'setup_logging2' creates two separate log files, one for
# stderr and one for stdout. This makes it easy to detect errors
# (if there's lots of non-error noise on STDOUT), but it might make it
# hard to know when/where the error was printed during the program's life time.
#
# NOTE:
# when STDERR and STDOUT are different streams, STDERR is usually not buffered
# and printed quickly, while STDOUT is buffered and printed slowly, thus the
# order of the messages might seem 'incorrect'.
#
# See 'log-to-file1.sh' for an alternative (saving STDOUT and STDERR
# into one merged file).
#

die()
{
    BASE=$(basename "$0")
    echo "$BASE: error: $@" >&2
    exit 1
}

setup_logging2()
{
    logprefix="$1"
    test -z "$logprefix" \
        && die "internal error: missing log filename parameter"

    # Create a tmp directory, to store the fifo
    __pipedir=$(mktemp -d -t log.XXXXXX) \
        || die "failed to create tmp directory"

    # Create the fifo file
    mkfifo "${__pipedir}/log-fifo-out" \
        || die "failed to create fifo"
    mkfifo "${__pipedir}/log-fifo-err" \
        || die "failed to create fifo"

    # Run 'tee' in the background, duplicating
    # the input (from the fifo) to both STDOUT and the log file
    tee "${logprefix}.stdout.log" < "${__pipedir}/log-fifo-out" &

    # duplicate the input to both file and STDERR
    tee "${logprefix}.stderr.log" < "${__pipedir}/log-fifo-err" >&2 &

    # Re-exec this shell instance, merging STDERR into STDOUT
    # and redirecting STDOUT into the fifo
    exec >"${__pipedir}/log-fifo-out" 2>"${__pipedir}/log-fifo-err"

    # Delete the FIFO and the temp dir -
    # no harm since the the fifo's file-descriptior is
    # held open by 'tee'. Saves the trouble of cleanup on exit.
    rm "${__pipedir}/log-fifo-out" "${__pipedir}/log-fifo-err"\
        || die "failed to cleanup fifo files"
    rmdir "${__pipedir}" \
        || die "failed to cleanup tmp dir"
}


# Setup logging into a file with a time stamp
log=program-$(date +%F-%H%M%S)
setup_logging2 "$log"

# Simulate some output both to STDOUT and STDERR
echo "Logging Example - anything you see printed to the terminal"
echo " is also saved in log files:"
echo "   stdout: $log.stdout.log"
echo "   stderr: $log.stderr.log"

echo "Hello (Stdout)"
echo "Hello (stderr)" >&2

# Simulate potential error messages to stdout/err.
# NOTE:
#  stdout (the 'echo') will be saved in one file,
#  while the error (from 'cp') will be saved in another.
#  this makes it easy to spot errors, but might make it harder
#  to understand the context (unless progress messages are also printed
#  to STDERR).
echo "Trying to copy non-existing file (which will fail):"
cp "/foo/bar" "/bar/baz"