set command in Linux

The set command in Linux is used to set or unset shell options and positional parameters. It can enable options like -x for debugging or -e for exiting immediately when a command returns a non-zero status. By setting positional parameters, you can assign values to variables within a script. This command is essential for customizing the behavior of your shell environment and controlling the flow of your scripts.

set Syntax:

set [option] [parameter]

Linux set Options:

Option	Description
-e	Exit immediately if a command exits with a non-zero status.
-u	Treat unset variables as an error when substituting.

set Parameters:

Parameter	Description
variable	Specifies the variable to be set.

Caution

Exercise caution when using the set command as it can alter the behavior of the shell session, especially with options like -e and -u which can impact script execution and error handling.

How to use set command:

Set a Bash Variable

fav_color=blue

Defines a Bash variable named “fav_color” with the value “blue”.

List All Variables

set

Displays all variables, functions, and positional parameters in the current shell session.

Set an Array Variable

fruits=(apple orange banana)

Defines an array variable named “fruits” containing three elements: apple, orange, and banana.

Set a Variable with Command Output

current_date=$(date)

Assigns the output of the “date” command to a variable named “current_date”.

Set Read-Only Variable

readonly user="john"

Defines a read-only variable named “user” with the value “john”, preventing it from being changed.

Unset a Variable

unset fav_color

Removes the variable “fav_color” from the shell session.

Export a Variable

export PATH=$PATH:/opt/bin

Adds “/opt/bin” to the PATH variable, making it accessible to all child processes.

Set a Default Value for an Unset Variable

echo ${name:-"Anonymous"}

Prints the value of the variable “name,” or “Anonymous” if the variable is unset or null.

Tip

When using the set command in Linux, make sure to familiarize yourself with the various options and arguments available to customize its behavior according to your requirements. Experiment with different combinations to fully understand the capabilities of the set command.

How do I use set in Linux?

To use the set command in Linux, execute the following command:

set --option <value>

How do I enable debugging with set in bash?

To enable debugging with the set command in bash, use the following command:

set -x

How do I show all shell input with set in Linux?

To display all shell input using the set command in Linux, run:

set -v

How do I check if a variable is unset with set in bash?

To check whether a variable is unset using the set command in bash, you can use:

set -u

How do I use the noclobber option with set in Linux?

To prevent overwriting existing files with the noclobber option using the set command in Linux, utilize:

set -o noclobber

How do I ignore the errexit setting with set in bash?

To ignore the errexit setting using the set command in bash, you can apply:

set +e

How do I view current shell options with set in Linux?

To view the current shell options using the set command in Linux, type:

set -o

How do I disable tracing with set in bash?

To disable tracing when using the set command in bash, input the following command:

set +x

How do I find the current value of a specific option with set in Linux?

To determine the current value of a specific option using the set command in Linux, you can check by running:

shopt -o <option>

Applications of the set command

• Managing shell options and attributes
• Displaying or modifying shell variables and functions