Bash script template (incl. logging functions)

bash-template.sh

#!/bin/bash

#################################
# Constants / global variables
#################################
LOGFILE='example.log'
LOGLEVEL='INFO'

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

# Logging functions
function log_output {
  echo `date "+%Y/%m/%d %H:%M:%S"`" $1"
  echo `date "+%Y/%m/%d %H:%M:%S"`" $1" >> $LOGFILE
}

function log_debug {
  if [[ "$LOGLEVEL" =~ ^(DEBUG)$ ]]; then
    log_output "DEBUG $1"
  fi
}

function log_info {
  if [[ "$LOGLEVEL" =~ ^(DEBUG|INFO)$ ]]; then
    log_output "INFO $1"
  fi
}

function log_warn {
  if [[ "$LOGLEVEL" =~ ^(DEBUG|INFO|WARN)$ ]]; then
    log_output "WARN $1"
  fi
}

function log_error {
  if [[ "$LOGLEVEL" =~ ^(DEBUG|INFO|WARN|ERROR)$ ]]; then
    log_output "ERROR $1"
  fi
}

# Some other helper functions
# ...

# Help output
function usage {
  echo
  echo "This is a Bash script template"
  echo "Usage: ./example.sh -l <logfile> -L <loglevel>"
  echo "Example: ./example.sh -l example.log -L INFO"
  echo
}

#################################
# Main
#################################

# Get input parameters
while [[ "$1" != "" ]]; do
  case $1 in
      -l | --logfile )        shift
                              LOGFILE=$1
                              ;;
      -L | --loglevel )       shift
                              LOGLEVEL=$1
                              ;;
      -h | --help )           usage
                              exit
                              ;;
      * )                     usage
                              exit 1
  esac
  shift
done

# Check input parameters and other required conditions

# Check if "docker" is installed
command -v docker >/dev/null 2>&1 || \
  (log_error "Docker is required. Check if it's installed and available in the PATH." \
  && exit 1)

# Check if a param is set to a valid value
if [[ ! "$LOGLEVEL" =~ ^(DEBUG|INFO|WARN|ERROR)$ ]]; then
  log_error "Logging level needs to be DEBUG, INFO, WARN or ERROR."
  exit 1
fi

# Bash script logic starts here...