bash3boilerplate/main.sh

#!/usr/bin/env bash
#
# Template to write better bash scripts. More info: http://kvz.io
# Version 0.0.1
#
# Usage:
#  LOG_LEVEL=7 ./template.sh first_arg second_arg
#
# Licensed under MIT
# Copyright (c) 2013 Kevin van Zonneveld
# http://twitter.com/kvz
#

### Configuration
#####################################################################

# Environment variables
[ -z "${LOG_LEVEL}" ] && LOG_LEVEL="6" # 7 = debug -> 0 = emergency

# Commandline options. This defines the usage page, and is used to parse cli opts & defaults from.
# the parsing is unforgiving so be precise in your syntax:
read -r -d '' usage <<-'EOF'
  -f   [arg] Filename to process.
  -t   [arg] Location of tempfile. Default="/tmp/x"
  -d         Enables debug mode
  -h         This page
EOF

# Set magic variables for current FILE & DIR
__FILE__="$(test -L "$0" && readlink "$0" || echo "$0")"
__DIR__="$(cd "$(dirname "${__FILE__}")"; echo $(pwd);)"


### Functions
#####################################################################

function _fmt ()      {
  color_ok="\x1b[32m"
  color_bad="\x1b[31m"

  color="${color_bad}"
  if [ "${1}" = "debug" ] || [ "${1}" = "info" ] || [ "${1}" = "notice" ]; then
    color="${color_ok}"
  fi

  color_reset="\x1b[0m"
  if [ "${TERM}" != "xterm" ] || [ -t 1 ]; then
    # Don't use colors on pipes or non-recognized terminals
    color=""
    color_reset=""
  fi
  echo -e "$(date -u +"%Y-%m-%d %H:%M:%S UTC") ${color}$(printf "[%9s]" ${1})${color_reset}";
}
function emergency () { echo "$(_fmt emergency) ${@}" || true; exit 1; }
function alert ()     { [ "${LOG_LEVEL}" -ge 1 ] && echo "$(_fmt alert) ${@}" || true; }
function critical ()  { [ "${LOG_LEVEL}" -ge 2 ] && echo "$(_fmt critical) ${@}" || true; }
function error ()     { [ "${LOG_LEVEL}" -ge 3 ] && echo "$(_fmt error) ${@}" || true; }
function warning ()   { [ "${LOG_LEVEL}" -ge 4 ] && echo "$(_fmt warning) ${@}" || true; }
function notice ()    { [ "${LOG_LEVEL}" -ge 5 ] && echo "$(_fmt notice) ${@}" || true; }
function info ()      { [ "${LOG_LEVEL}" -ge 6 ] && echo "$(_fmt info) ${@}" || true; }
function debug ()     { [ "${LOG_LEVEL}" -ge 7 ] && echo "$(_fmt debug) ${@}" || true; }

function help () {
  echo ""
  echo " ${@}"
  echo ""
  echo "  ${usage}"
  echo ""
  exit 1
}

function cleanup_before_exit () {
  info "Cleaning up. Done"
}
trap cleanup_before_exit EXIT


### Parse commandline options
#####################################################################

# Translate usage string -> getopts arguments, and set $arg_<flag> defaults
while read line; do
  opt="$(echo "${line}" |awk '{print $1}' |sed -e 's#^-##')"
  if ! echo "${line}" |egrep '\[.*\]' >/dev/null 2>&1; then
    init="0" # it's a flag. init with 0
  else
    opt="${opt}:" # add : if opt has arg
    init=""  # it has an arg. init with ""
  fi
  opts="${opts}${opt}"

  varname="arg_${opt:0:1}"
  if ! echo "${line}" |egrep '\. Default=' >/dev/null 2>&1; then
    eval "${varname}=\"${init}\""
  else
    match="$(echo "${line}" |sed 's#^.*Default=\(\)#\1#g')"
    eval "${varname}=\"${match}\""
  fi
done <<< "${usage}"

# Reset in case getopts has been used previously in the shell.
OPTIND=1

# Overwrite $arg_<flag> defaults with the actual CLI options
while getopts "${opts}" opt; do
  line="$(echo "${usage}" |grep "\-${opt}")"


  [ "${opt}" = "?" ] && help "Invalid use of script: ${@} "
  varname="arg_${opt:0:1}"
  default="${!varname}"

  value="${OPTARG}"
  if [ -z "${OPTARG}" ] && [ "${default}" = "0" ]; then
    value="1"
  fi

  eval "${varname}=\"${value}\""
  debug "cli arg ${varname} = ($default) -> ${!varname}"
done

shift $((OPTIND-1))

[ "$1" = "--" ] && shift


### Switches
#####################################################################

# debug mode
if [ "${arg_d}" = "1" ]; then
  set -x
  LOG_LEVEL="7"
fi

# help mode
if [ "${arg_h}" = "1" ]; then
  help "Help using ${0}"
fi


### Validation
#####################################################################

[ -z "${arg_f}" ]     && help   "Setting a filename with -f is required"
[ -z "${LOG_LEVEL}" ] && emergency "Cannot continue without loglevel. "


### Runtime
#####################################################################

# Exit on error. Append ||true if you expect an error.
# set -e is safer than #!/bin/bash -e because that is nutralised if
# someone runs your script like `bash yourscript.sh`
set -e

# Bash will remember & return the highest exitcode in a chain of pipes.
# This way you can catch the error in case mysqldump fails in `mysqldump |gzip`
set -o pipefail

debug "Info useful to developers for debugging the application, not useful during operations."
info "Normal operational messages - may be harvested for reporting, measuring throughput, etc. - no action required."
notice "Events that are unusual but not error conditions - might be summarized in an email to developers or admins to spot potential problems - no immediate action required."
warning "Warning messages, not an error, but indication that an error will occur if action is not taken, e.g. file system 85% full - each item must be resolved within a given time. This is a debug message"
error "Non-urgent failures, these should be relayed to developers or admins; each item must be resolved within a given time."
critical "Should be corrected immediately, but indicates failure in a primary system, an example is a loss of a backup ISP connection."
alert "Should be corrected immediately, therefore notify staff who can fix the problem. An example would be the loss of a primary ISP connection."
emergency "A \"panic\" condition usually affecting multiple apps/servers/sites. At this level it would usually notify all tech staff on call."