Shell Options

PAGER='less "+/^ *The list of shopt"' man bash Opens the bash man page to the shopt options and descriptions.

• shopt -p: Display all settable options.

set

The set built-in command is used to set or unset shell options and positional parameters. You can change a lot of behaviors of the shell using set.

set Options and Arguments

• set -o option: Enables an option.
• set +o option: Disables an option.
• set --: Unsets all positional parameters.
• set -: Turns off -v and -x options, among others.

Some shell options have shorthands that can be used (e.g., set -e instead of set -o errexit).

• set -e: Exit immediately if a command exits with a non-zero status.
  • Same as set -o errexit
• set -u: Treat unset variables as an error when substituting.
  • Same as set -o nounset
• set -o pipefail: If any command in a pipeline fails, the whole pipeline fails.
  • Failure in this case is any non-zero exit status.
• set -x: Print commands and their arguments as they are executed.
  • Usually used for debugging purposes.
• set -o vi: Use vi keybindings for regular command-line interactions.

set Uses

• set -e: Useful in scripts where you want to ensure that errors stop the script.
• set -u: Good for debugging uninitialized variables.
• set -x: Helpful for debugging scripts.

shopt

The shopt built-in allows you to change additional shell optional behavior. It's more flexible than set in some ways.

shopt Options and Arguments

• shopt -s option: Enables (-sets) an option.
• shopt -u option: Disables (-unsets) an option.
• shopt -q: Quiet mode. Nothing is output.
  • Can be used to check if an option is set. It will return zero if all options are set, and non-zero if there are any that are unset.

shopt Uses

• shopt -s nullglob: Useful when you want patterns that could match filenames to expand to an empty string when no filenames match.

• shopt -s dotglob: Useful when you want patterns to include files that start with a dot (.).

Non-Exhaustive List of Shell Options

Shell options for set

• -e, errexit: Exit on error.
• -f, noglob: Disable filename expansion.
• -H, histexpand: Enable ! style history substitution.
• -u, nounset: Treat unset variables as an error.
• -x, xtrace: Debug mode.
• -o: Specify a named option.

Run help set for a full list.

Shell options for shopt

• cdspell: Autocorrects minor spelling errors in a cd command.
• checkhash: Checks that commands found in hash tables exist.
• cmdhist: Save multi-line commands in the history as a single line.
• dotglob: Includes dot files in pathname expansion.
• extglob: Enables extended pattern matching.
• nullglob: Allows patterns to return a null string if no match is found.

Check man bash for a full list under the SHELL BUILTIN COMMANDS section.