kdlug/bash

Bash Best Practices

Exit a script when a command fails

set -o errexit 
# OR
set -e

-e indicates that from that point forward, all errors will trigger an EXIT signal.

Exit a script when using undeclared variable

set -o nounset
# OR
set -u

Use $(cmd) instead of legacy ‘cmd’ for Substitution

# legacy
user=`echo `$USER`
# recommended
user=$(echo $USER)

Use Read-only to Declare Static Variables

readonly passwd_file=”/etc/passwd”
readonly group_file=”/etc/group”

Use Uppercase Names for ENVIRONMENT Variables and Lowercase for Custom Variables

All bash environment variables are named with uppercase letters, therefore use lowercase letters to name your custom variables to avoid variable name conflicts.

Add help

It's useful to include a -h or --help flag which prints usage information about the script

if [[ ${#@} -ne 0 ]] && [[ "${@#"--help"}" = "" ]]; then
  printf -- '...help...\n';
  exit 0;
fi;

Check if command is available

Command is a bash built-in.

command -v binary-name

docker=$(command -v docker);
if [ "$docker" != "0" ]; then
  print -e -- 'Docker is not installed';
  exit 127;

Use exit codes

127 - command not found
0 - success
1 - general errors such as "divide by zero" and other impermissible operations

Show steps which are done using check/cross mark

echo -e '\u2718' # check mark
echo -e '\u2714' # cross mark

echo -e '\u2717' # heavy check mark
echo -e '\u2713' # heavy cross mark