template.sh

#!/bin/bash
#
#   <script_name>   <desc>
#   Author:         <author>
#

set -o errtrace

readonly LOG_DIR="/tmp/log"
readonly LOG_FILE="output.log"

assert() {
    [ -d $LOG_DIR ] \
        || mkdir -p $LOG_DIR
}

configure_logger() {
    local timeformat="+%Y%m%d_%H%M%S"
    local log_endpoint="${LOG_DIR}/${LOG_FILE}"

    coproc LOGGER {
        while read -r line; do
            echo "[$(date $timeformat)] $line" >> $log_endpoint
        done
    }
    exec 3>&1
    exec 4>&2
    exec 1>&${LOGGER[1]}
    exec 2>&1
}

restore_exec_redirect() {
    exec 1>&3
    exec 2>&4
}

logging() {
    if [ $? -ne 0 ]; then
        echo "failed on: $BASH_COMMAND"
        restore_exec_redirect
        echo "failed on: $BASH_COMMAND"
        exit 1
    else
        echo "+ $BASH_COMMAND"
    fi
}

helloworld() {
    echo "hello world!"
}

sampletask() {
    echo "first step"
    echo "second step"
}

main() {
    assert
    configure_logger
    trap "logging" DEBUG ERR
    helloworld
    sampletask
    echo "end"
}

main