Man Set

Configuring Shell Options and Variables with `set`

Understanding the `set` Builtin

The `set` builtin is a powerful tool in the shell that allows you to manipulate shell options, positional parameters, and shell variables. It offers a wide range of functionalities, including: * Changing the value of shell options * Setting positional parameters * Displaying the names and values of shell variables * Marking variables for export

Basic Syntax

The basic syntax of `set` is as follows: ```bash set [-abefhkmnptuvxBCEHOPT] [-] [var=value]... [--] [args...] ```

Options

The `set` builtin supports numerous options that control its behavior: * `-a`: Mark variables modified or created for export. * `-b`: Display the arguments and values of shell variables. * `-e`: Exit when any command in a pipeline returns a non-zero exit status. * `-f`: Disable globbing for arguments. * `-h`: Display a help message. * `-k`: Save traps in the execution environment. * `-m`: Monitor mode - display commands being executed along with their exit status. * `-n`: Read commands but do not execute them. * `-o`: Display the names and values of shell options. * `-p`: Display positional parameters. * `-t`: Check for unquoted parameter expansions. * `-u`: Exit when accessing an undefined variable. * `-v`: Print shell input lines as they are read.

Parameters

The `set` builtin can take a variety of parameters: * `var=value`: Sets the value of the shell variable `var` to `value`. * `-`: Reset positional parameters. * `--`: End of option processing. Any subsequent arguments are treated as positional parameters.

Examples

### Changing Shell Options ```bash # Turn on the -x and -v options set -x -v # Execute a command ls -l ``` ### Setting Positional Parameters ```bash # Set positional parameter 1 to the value of x, even if it begins with - or . set 1=x # Display the positional parameters echo "$#" "$1" ``` ### Displaying Shell Variables ```bash # Display the names and values of all shell variables set # Display the value of a specific variable echo "$PATH" ``` ### Marking Variables for Export ```bash # Mark the PATH variable for export set -a PATH ```

Conclusion

The `set` builtin is an indispensable tool for customizing and managing the shell environment. By understanding its syntax and options, you can manipulate shell options, positional parameters, and shell variables with precision, enhancing your workflow and optimizing script execution.