Bash script template

template.sh

#!/bin/bash

################################################################################
#                              scriptTemplate  
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#                                                                              #
#  Copyright (C) 2020 Maksym Voitko                                            #
#  max.voitko@gmail.com                                                        #
#                                                                              #
#  This program is free software; you can redistribute it and/or modify        #
#  it under the terms of the GNU General Public License as published by        #
#  the Free Software Foundation; either version 2 of the License, or           #
#  (at your option) any later version.                                         #
#                                                                              #
#  This program is distributed in the hope that it will be useful,             #
#  but WITHOUT ANY WARRANTY; without even the implied warranty of              #
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the               #
#  GNU General Public License for more details.                                #
#                                                                              #
#  You should have received a copy of the GNU General Public License           #
#  along with this program; if not, write to the Free Software                 #
#  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA   #
#                                                                              #
################################################################################
################################################################################
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# Run in debug mode, if set
if [ "${debug}" == "1" ]; then
  set -x
fi

# Exit on empty variable
if [ "${strict}" == "1" ]; then
  set -o nounset
fi

set -o errexit          # Exit immediately when it encounters a non-zero exit code from an executed command
set -o errtrace         # Make sure any error trap is inherited       
set -o pipefail         # Use last non-zero exit code in a pipeline

log_level_for()
{
  case "${1}" in
    "error")
      echo 1
      ;;

    "warn")
      echo 2
      ;;

    "debug")
      echo 3
      ;;

    "info")
      echo 4
      ;;
    *)
      echo -1
      ;;
  esac
}

current_log_level()
{
  log_level_for "${LOG_LEVEL}"
}

error()
{
  [ $(log_level_for "error") -le $(current_log_level) ] &&  echo "${1}" >&2
}

warn()
{
  [ $(log_level_for "warn") -le $(current_log_level) ] &&  echo "${1}" >&2
}

debug()
{
  [ $(log_level_for "debug") -le $(current_log_level) ] &&  echo "${1}" >&2
}

info()
{
  [ $(log_level_for "info") -le $(current_log_level) ] &&  echo "${1}" >&2
}

# DESC: Handler for unexpected errors
# ARGS: $1 (optional): Exit code (defaults to 1)
# OUTS: None
function script_trap_err() {
    local exit_code=1

    # Disable the error trap handler to prevent potential recursion
    trap - ERR

    # Consider any further errors non-fatal to ensure we run to completion
    set +o errexit
    set +o pipefail

    # Validate any provided exit code
    if [[ ${1-} =~ ^[0-9]+$ ]]; then
        exit_code="$1"
    fi

    # Output debug data if in Cron mode
    if [[ -n ${cron-} ]]; then
        # Restore original file output descriptors
        if [[ -n ${script_output-} ]]; then
            exec 1>&3 2>&4
        fi

        # Print basic debugging information
        printf '%b\n' "$ta_none"
        printf '***** Abnormal termination of script *****\n'
        printf 'Script Path:            %s\n' "$script_path"
        printf 'Script Parameters:      %s\n' "$script_params"
        printf 'Script Exit Code:       %s\n' "$exit_code"

        # Print the script log if we have it. It's possible we may not if we
        # failed before we even called cron_init(). This can happen if bad
        # parameters were passed to the script so we bailed out very early.
        if [[ -n ${script_output-} ]]; then
            printf 'Script Output:\n\n%s' "$(cat "$script_output")"
        else
            printf 'Script Output:          None (failed before log init)\n'
        fi
    fi

    # Exit with failure status
    exit "$exit_code"
}

# DESC: Handler for exiting the script
# ARGS: None
# OUTS: None
function script_trap_exit() {
    cd "$orig_cwd"

    # Remove Cron mode script log
    if [[ -n ${cron-} && -f ${script_output-} ]]; then
        rm "$script_output"
    fi

    # Remove script execution lock
    if [[ -d ${script_lock-} ]]; then
        rmdir "$script_lock"
    fi

    # Restore terminal colours
    printf '%b' "$ta_none"
}

# DESC: Exit script with the given message
# ARGS: $1 (required): Message to print on exit
#       $2 (optional): Exit code (defaults to 0)
# OUTS: None
# NOTE: The convention used in this script for exit codes is:
#       0: Normal exit
#       1: Abnormal exit due to external error
#       2: Abnormal exit due to script error
function script_exit() {
    if [[ $# -eq 1 ]]; then
        printf '%s\n' "$1"
        exit 0
    fi

    if [[ ${2-} =~ ^[0-9]+$ ]]; then
        printf '%b\n' "$1"
        # If we've been provided a non-zero exit code run the error trap
        if [[ $2 -ne 0 ]]; then
            script_trap_err "$2"
        else
            exit 0
        fi
    fi

    script_exit 'Missing required argument to script_exit()!' 2
}

# DESC: Parameter parser
# ARGS: $@ (optional): Arguments provided to the script
# OUTS: Variables indicating command-line parameters and options
function parse_params() {
    local param
    while [[ $# -gt 0 ]]; do
        param="$1"
        shift
        case $param in
            -h | --help)
                script_usage
                exit 0
                ;;
            -v | --verbose)
                verbose=true
                ;;
            -nc | --no-colour)
                no_colour=true
                ;;
            -cr | --cron)
                cron=true
                ;;
            *)
                script_exit "Invalid parameter was provided: $param" 1
                ;;
        esac
    done
}