system programing in bash

timestamp.sh

#!/bin/bash

# This script is designed to make sure that a signal delivered to it
# is propagated to a subshell running the program feeding the lines to
# be timestamped.  The usual command line is:
#
#     timestamp command ... arguments ...

# The 'builtin' specifications are not necessary, but are included to
# convey that what follows them are internal shell commands, so bash
# doesn't spawn subshells to run them.

# Start a subshell running "$@" (impitool ...) and read its stdout (<)
# from FD 3 (exec 3< ...).  Use (exec "$@) so the PID captured by $!
# is the command line "$@" (ipmitool ...) and not the bash process
# handling the command line.
#
exec 3< <(exec "$@")

# Trap HUP, INT, and TERM ($sn) to kill the subshell running "$@"
# (kill $!), then remove the $sn trap and kill this process ($$) with
# $sn so whatever is waiting for this process sees $sn in this
# process's exit status.
#
for sn in HUP INT TERM
do
    trap "builtin kill -$sn $!; trap $sn; builtin kill -$sn $$" $sn
done

# Read raw (-r) lines from FD 3 (-u3) into the variable $line, then
# print the line preceeded by a timestamp in brackets ([<ts>]: ...).
# The cut removes the 3 least significant digits of the nanosecond
# field (%N) formatted by date.
#
while IFS= read -r -u3 line
do
    builtin printf '[%s]: %s\n' \
        "$(date +%Y-%m-%dT%H:%M:%S.%N%:z | cut -c1-26,30-35)" \
        "$line"
done