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Bash Scripting Conventions

Scripting conventions are needed, especially with Bash, as things can get rather wild if not. Follow them, they try to avoid havoc and chaos.


  • Include a #!/bin/bash header as the first line of your file:
  • You may have a header written in the style of:
# written by Dan Fruehauf <malkodan@gmail.com>
  • Indent everything with tabs and not with spaces!
    • And if you are indenting with spaces, be consistent with it!
  • If using for any reason in your script rm -rf $VARIABLE, make sure $VARIABLE is not empty, and not '/':
if [ x"$VARIABLE" != x ] && [ "$VARIABLE" != "/" ]; then
	rm -rf --preserve-root $VARIABLE
	echo "Critical: tried to delete '$VARIABLE'" 1>&2
	exit 1
  • In case there is a use for a temporary file, use mktemp to generate it and make sure to remove it:
local temp_filename=`mktemp`
<< operations with $temp_filename >>
rm -f $temp_filename
# what NOT to do:
local temp_shitty_filename=/tmp/i.am.idiot.$$


  • Avoid global variable as much as you can, although usually common in bash scripts try to avoid them.
  • Avoid using hardcoded constants, it is better to have a read only global variable for that purpose.
  • If you do use global variables after all, document their use specifically, and declare them with capital letters:
  • Use the keyword local to declare variables locally in functions. Variables declared in functions will always be with lowercase letters:
local variable_inside_function="some text"
  • Use declare -r or local -r to declare read only variables
    • Alternatively use readonly to declare a read only variable
  • Use declare -i or local -i to declare integer variables, it is a lot safer
# global read variable
declare -r READ_ONLY_VARIABLE=example
# global read only integer variable
# local integer variable
local -i number_of_people_in_the_room=4


  • Create functions with clear names and specific objectives. Avoid bloated functions.
  • Function names will be in lowercase letters and underscores will separate the words, e.g.:
make_home_directory_for_user() {
  • Every script should have a main() function in it's end, followed by a call to it:
main() {

main "$@"
  • DO NOT write any code not in a function (except for the call to main() of course)
  • Use function headers to describe it's parameters and use shift to retrieve variables. Avoid using $1, $2 etc, unless the function is really small, then the use of "$@" is allowed.
# $1 - user name
# $2 - user's home directory
# "$@" - files to copy
copy_files_to_user_homedir() {
	local username=$1; shift
	local user_homedir=$1; shift
	for file in "$@"; do
		cp -a $file $user_homedir
		chown $username $user_homedir/`basename $file`
  • Return values from functions are 0 for success or anything else for failure:
# this function bakes a cake
# $1 - temperature
bake_cake() {
	local -i temperature=$1; shift
	local -i retval=0
	if [ $temperature -gt 400 ]; then
		echo "Cake has burnt!"
		echo "Cake is alright"
	return $retval
  • Use a standard variable ($retval) to calculate the return value
  • Accumulating a return value in a function can be done by adding to a $retval variable:
# this function does a few things
# "$@" - things to do
do_a_few_things() {
	local -i retval=0
	local thing
	for thing in "$@"; do
		echo -n "Doing '$thing'..."
		let retval=$retval+$?
		echo "Done!"
	return $retval
  • Returning a few values from a function can be done either by returning a comma (or other character) separated value to STDOUT or by assigning "reference" variables:
# this function returns 3 random numbers
random3() {

local random_number_tuple=`random3`
local -i random_number1=`echo $random_number_tuple | cut -d, -f1`
local -i random_number2=`echo $random_number_tuple | cut -d, -f2`
local -i random_number3=`echo $random_number_tuple | cut -d, -f3`

# or by passing variables "by reference"
# it is using global variables indirectly, however we unset them
# after use, so it's not THAT bad...
# this function returns 3 random numbers
# $1 - return value #1
# $2 - return value #2
# $3 - return value #3
random3() {
	local retval_1=$1; shift
	local retval_2=$1; shift
	local retval_3=$1; shift

	eval $retval_1=\$RANDOM
	eval $retval_2=\$RANDOM
	eval $retval_3=\$RANDOM

random3 random_number1 random_number2 random_number3
echo $random_number1 $random_number2 $random_number3
# don't forget to unset these as they will be global...
unset random_number1 random_number2 random_number3
  • Private functions which shouldn't be called or "exported" should usually start with an underscore:
# public function
hello_world() {

# private function
_hello_world_impl() {
	echo "Hello world!"
  • When sourcing another bash file, never use ., but the source keyword, that makes things easier when auditing code and grepping for external files:
# avoid the following
. /etc/bashrc
# this is OK
source /etc/bashrc


Use comments where applicable. Do not capitalize comments - this will make it easier to grep for things if necessary:

# This is a capitalized comment - avoid
# this is an OK comment :)


  • In case a script was misused, create a usage() function and have it's output go to stderr instead of stdout. This can be achieved by:
usage() {
	echo "Usage: "`basename $0`" parameters" 1>&2
	echo "Example: "`basename $0`" -a param -b -param" 1>&2
	exit 2
  • Always parse options with getopts. It is safer and friendlier for the user. Here is a snippet for getopts:
# main
main() {
	# parse getopts options
	local tmp_getopts=`getopt -o hab:A:B: --long help,aopt,bopt:,Aopt:,Bopt: -- "$@"`
	[ $? != 0 ] && usage
	eval set -- "$tmp_getopts"

	# option_A and option_B takes a parameter
	# option_a and option_b don't
	local option_a option_b option_A option_B
	while true; do
		case "$1" in
			-h|--help) usage;;
			-a|--aopt) option_a=yes; shift 1;;
			-b|--bopt) option_b=yes; shift 1;;
			-A|--Aopt) option_A=$2; shift 2;;
			-B|--Bopt) option_B=$2; shift 2;;
			--) shift; break;;
			*) usage;;

	# if option_a is mandatory, you can have something like
	[ x"$option_a" = x ] && usage
  • In case there's required user intervention, you MAY create a neat dialog using dialog, DON'T BE LAZY if you want people to use your scripts:
if dialog --yesno "Are you sure you want to wipe out your whole hard drive?" 0 0; then
	echo "OMG, FAIL."; exit 2
	echo "Good choice, mate."