#!/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 a log file (in addition to also outputing it to the
# original STDOUT/STDERR (e.g. the terminal).
#
# The function 'setup_logging1' MERGES stdout and stderr into one log file.
# This makes it easier to review later, but loses the distinction between
# what was printed to STDOUT and what was printed to STDERR.
# depending on your application, this might be acceptable.
#
# See 'log-to-file2.sh' for an alternative (saving STDOUT and STDERR into
# two separate files).

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

setup_logging1()
{
    logfile="$1"
    test -z "$logfile" \
        && 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" \
        || die "failed to create fifo"

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

    # Re-exec this shell instance, merging STDERR into STDOUT
    # and redirecting STDOUT into the fifo
    exec >"${__pipedir}/log-fifo" 2>&1

    # 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 "${__pipedir}/log-fifo" \
        || die "failed to cleanup fifo file"
    rmdir "${__pipedir}" \
        || die "failed to cleanup tmp dir"
}


# Setup logging into a file with a time stamp
log=program-$(date +%F-%H%M%S).log
setup_logging1 "$log"

# Simulate some output both to STDOUT and STDERR
echo "Logging Example - anything you see printed to the terminal"
echo " is also saved in the file '$log'"

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

# Simulate potential error messages to stderr
echo "Trying to copy non-existing file (which will fail):"
cp "/foo/bar" "/bar/baz"