set - macOS

Overview

The set command in macOS is a versatile tool for managing shell variables and settings. It allows users to set, modify, and display variables, as well as configure various aspects of the shell environment.

Syntax

set [-e|-a|-u|-f|-h|-o|-v|-p|-x] [-bl|-E|-n|-t|-i] [-S STRING] [name[=value] ...]

Options/Flags

  • -e: Exit immediately if any command in a pipeline returns a non-zero status.
  • -a: Export all variables assigned in the current context.
  • -u: Treat unset variables as errors.
  • -f: Disable filename expansion.
  • -h: Display a help message.
  • -o: Display the current shell options.
  • -v: Print shell input lines as they are read.
  • -p: Print the current variable settings.
  • -x: Print the expanded commands before they are executed.
  • -bl: Interpret backslash-escaped characters literally.
  • -E: Set the POSIX environment.
  • -n: Read commands but do not execute them.
  • -t: Turn off interactive mode.
  • -i: Treat null input as an interactive shell.
  • -S STRING: Set the shell environment to STRING.

Examples

Set a variable:

set my_var="Hello World"

Export a variable:

set -a my_var

Print variable settings:

set -p

Disable filename expansion:

set -f

Execute commands without printing them:

set -n echo "This command won't be printed"

Common Issues

  • Unset variables: Using unset variables with -u enabled will cause an error. Use set -u with caution.
  • Mismatched quotes: Ensure proper quoting when setting variables with spaces or special characters.

Integration

set can be combined with other commands for advanced tasks:

  • Set environment variables: set -a; export PATH=$PATH:/new/path
  • Pass variables to scripts: my_script.sh $my_var
  • Create temporary variables: set -n my_temp_var=$(echo "Temporary data")
  • env: Display or set environment variables.
  • export: Export variables to the environment.
  • unset: Delete variables.
  • alias: Create shell aliases.