Bash usefull tips

example.sh

#! /bin/bash

#
# Script: example.sh
# Author: Example Author <autor@example.com>
# Description:
#   This script is an example for writing good bash script.
# Source: Gronono's Github Gist (https://gist.github.com/gronono/cbccbefdd93a3618ad400eb83cb50c4a)
# Changelog:
#   YYYY-MM-DD: some modifications
#   2022-01-11: Create this example.
#
#
# Edit this function to change script configuration
#
function configure() {
    # Change the log level 
    LOG_LEVEL=${LOG_LEVEL_DEBUG}
}

#
# Begin of the script
# ! DO NOT EDIT BELOW THIS LINE !
#

#
# Main function
#
function main() {
    debug "Log some debug"
    info "Log some information: ${SCRIPT_DIRECTORY}"
    warn "Log some warning"
    error "Log some error"
    test_command_exists echo
    try echo "Let's try something"
    fatal "Fatal error"
    exit 0
}

#
# Utilities
# see https://gist.github.com/gronono/cbccbefdd93a3618ad400eb83cb50c4a 
#

# Directory containing this file
# https://stackoverflow.com/a/1482133/2909535
SCRIPT_DIRECTORY=$(dirname "$(readlink -f "$0")")

# Some colors
NO_COLOR='\033[0m'
COLOR_RED='\033[0;31m'
COLOR_GREEN='\033[0;32m'
COLOR_YELLOW='\033[0;33m'
COLOR_GRAY='\033[0;90m'

# Log levels
LOG_LEVELS="debug info warn error"
# Variables LOG_COLOR are used dynamically
# shellcheck disable=SC2034
LOG_COLOR_DEBUG=${COLOR_GRAY}
# shellcheck disable=SC2034
LOG_COLOR_INFO=${NO_COLOR}
# shellcheck disable=SC2034
LOG_COLOR_WARN=${COLOR_YELLOW}
# shellcheck disable=SC2034
LOG_COLOR_ERROR=${COLOR_RED}
# Default log level before configure called
LOG_LEVEL="info"

# Display a message with some color
echo_with_color() (
    color=$1
    shift 1
    printf "%s$*${NO_COLOR}\n" "${color}"
)

#
# Strings
#
to_uppercase() (
    echo "$1" | tr '[:lower:]' '[:upper:]'
)

#
# Arrays
#
index_of() (
    index=0
    found=-1
    for i in $1; do
        if [ "$i" = "$2" ]; then
            found=$index;
            break;
        fi
        index=$((index+1))
    done
    echo $found
)

# 
# Logger
#
is_log_level_enabled() (
    actual_log_level_idx=$(index_of "$LOG_LEVELS" $LOG_LEVEL)
    message_log_level_idx=$(index_of "$LOG_LEVELS" "$1")
    [ "$message_log_level_idx" -ge "$actual_log_level_idx" ]
)

log() (
    this_log_level=$1
    shift 1
    is_log_level_enabled "${this_log_level}"
    enabled=$?
    if [ $enabled -eq 0 ]; then
        var_log_color=$(to_uppercase "LOG_COLOR_$this_log_level" | tr '[:lower:]' '[:upper:]')
        log_color=$(eval "echo \$${var_log_color}")
        echo_with_color "${log_color}" "$@"
    fi
)

# Log a message in debug mode
debug() ( log "debug" "$@"; )
# Log a message in info mode
info()  ( log "info" "$@"; )
# Log a message in warning mode
warn()  ( log "warn" "$@"; )
# Log a message in error mode (error are also written in stderr)
error() ( log "error" "$@" >&2; )
# Log a success message
success() ( echo_with_color "${COLOR_GREEN}" "$@"; )
# Log an error and exit the script
die() ( error "$*"; exit 1; )
# If the command failed, log the command and exit
try() ( "$@" || die "Command '$*' failed!"; )
# Test if a command exists or die
test_command_exists() ( command -v "$1" > /dev/null || die "Command '$1' not found!"; )

#
# Run script's instructions
#
configure
main "$@"