Linux set Command with Practical Examples

Introduction

In this lab, you will learn how to use the set command in Linux to manage shell variables and options. The lab covers understanding the purpose and syntax of the set command, modifying shell variables, and managing environment variables. The set command is a powerful tool for configuring and customizing the shell environment, and the practical examples provided in this lab will help you become proficient in its usage.

Linux Commands Cheat Sheet

Skills Graph

Understand the Purpose and Syntax of the set Command

In this step, you will learn about the purpose and syntax of the set command in Linux. The set command is used to set, unset, and display shell variables and options.

First, let's explore the syntax of the set command:

set [option] [variable[=value]]

Here, option represents the various options that can be used with the set command, and variable[=value] represents the shell variable you want to set or unset.

Some common options used with the set command include:

• -a: Automatically mark variables which are modified or created for export to the environment of subsequent commands.
• -e: Exit immediately if a command exits with a non-zero status.
• -u: Treat unset variables as an error when substituting.
• -x: Print commands and their arguments as they are executed.

To display all the currently set shell variables, you can simply run the set command without any arguments:

set

Example output:

BASH=/bin/bash
BASHOPTS=checkwinsize:cmdhist:complete_fullquote:expand_aliases:extglob:extquote:force_fignore:histappend:interactive_comments:progcomp:promptvars:sourcepath
BASH_ALIASES=()
BASH_ARGC=()
BASH_ARGV=()
BASH_CMDS=()
BASH_COMPLETION_COMPAT_DIR=/etc/bash_completion.d
BASH_LINENO=()
BASH_SOURCE=()
BASH_VERSINFO=([0]="5" [1]="1" [2]="4" [3]="1" [4]="release" [5]="x86_64-pc-linux-gnu")
BASH_VERSION='5.1.4(1)-release'
COLUMNS=80
COMP_WORDBREAKS=$' \t\n"\'><=;|&(:'
DIRSTACK=()
EUID=1000
GROUPS=()
HISTCONTROL=ignoreboth
HISTFILE=/home/labex/.bash_history
HISTFILESIZE=2000
HISTSIZE=1000
HOME=/home/labex
HOSTNAME=8d5d8d1f0a3f
HOSTTYPE=x86_64
IFS=$' \t\n'
LANG=en_US.UTF-8
LESSCLOSE='/usr/bin/lesspipe %s %s'
LESSOPEN='| /usr/bin/lesspipe %s'
LINES=24
LOGNAME=labex
LS_COLORS='rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:mi=00:su=37;41:sg=30;43:ca=30;41:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01;31:*.arc=01;31:*.arj=01;31:*.taz=01;31:*.lha=01;31:*.lz4=01;31:*.lzh=01;31:*.lzma=01;31:*.tlz=01;31:*.txz=01;31:*.tzo=01;31:*.t7z=01;31:*.zip=01;31:*.z=01;31:*.dz=01;31:*.gz=01;31:*.lrz=01;31:*.lz=01;31:*.lzo=01;31:*.xz=01;31:*.zst=01;31:*.tzst=01;31:*.bz2=01;31:*.bz=01;31:*.tbz=01;31:*.tbz2=01;31:*.tz=01;31:*.deb=01;31:*.rpm=01;31:*.jar=01;31:*.war=01;31:*.ear=01;31:*.sar=01;31:*.rar=01;31:*.alz=01;31:*.ace=01;31:*.zoo=01;31:*.cpio=01;31:*.7z=01;31:*.rz=01;31:*.cab=01;31:*.wim=01;31:*.swm=01;31:*.dwm=01;31:*.esd=01;31:*.jpg=01;35:*.jpeg=01;35:*.mjpg=01;35:*.mjpeg=01;35:*.gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35:*.xbm=01;35:*.xpm=01;35:*.tif=01;35:*.tiff=01;35:*.png=01;35:*.svg=01;35:*.svgz=01;35:*.mng=01;35:*.pcx=01;35:*.mov=01;35:*.mpg=01;35:*.mpeg=01;35:*.m2v=01;35:*.mkv=01;35:*.webm=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*.mp4v=01;35:*.vob=01;35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35:*.flc=01;35:*.avi=01;35:*.fli=01;35:*.flv=01;35:*.gl=01;35:*.dl=01;35:*.xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.cgm=01;35:*.emf=01;35:*.ogv=01;35:*.ogx=01;35:*.aac=00;36:*.au=00;36:*.flac=00;36:*.m4a=00;36:*.mid=00;36:*.midi=00;36:*.mka=00;36:*.mp3=00;36:*.mpc=00;36:*.ogg=00;36:*.ra=00;36:*.wav=00;36:*.oga=00;36:*.opus=00;36:*.spx=00;36:*.xspf=00;36:'
MACHTYPE=x86_64-pc-linux-gnu
MAILCHECK=60
OLDPWD=/home/labex
OPTERR=1
OPTIND=1
OSTYPE=linux-gnu
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
PIPESTATUS=([0]="0")
PPID=1
PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '
PS2='> '
PS4='+ '
PWD=/home/labex/project
RANDOM=1836
READLINE_LINE=
READLINE_POINT=0
SHELL=/bin/bash
SHELLOPTS=braceexpand:hashall:interactive-comments:progcomp
SHLVL=1
SSH_CLIENT='172.17.0.1 52390 22'
SSH_CONNECTION='172.17.0.1 52390 172.17.0.2 22'
SSH_TTY=/dev/pts/0
TERM=xterm-256color
UID=1000
UPTIME_DAYS=0
UPTIME_HOURS=0
UPTIME_MINUTES=2
UPTIME_SECONDS=123
USER=labex
XDG_DATA_DIRS=/usr/local/share:/usr/share:/var/lib/snapd/desktop
XDG_RUNTIME_DIR=/run/user/1000
XDG_SESSION_ID=1
_=/usr/bin/env

As you can see, the set command displays all the currently set shell variables, including environment variables and shell options.

Now, let's explore how to use the set command to manage shell variables and options.

Modify Shell Variables Using the set Command

In this step, you will learn how to modify shell variables using the set command.

First, let's create a new shell variable:

set MYVAR="Hello, World!"

Now, let's verify that the variable was created correctly:

echo $MYVAR

Example output:

Hello, World!

You can also use the set command to modify the value of an existing shell variable:

MYVAR="Goodbye, World!"
set MYVAR

Example output:

MYVAR="Goodbye, World!"

To unset a shell variable, you can use the -u option with the set command:

set -u MYVAR
echo $MYVAR

Example output:

bash: MYVAR: unbound variable

As you can see, the MYVAR variable is now unset, and attempting to access it results in an error.

Finally, let's explore how to make a shell variable read-only using the -a option:

set -a READONLY_VAR="This variable is read-only"
READONLY_VAR="New value"

Example output:

bash: READONLY_VAR: readonly variable

In this example, we made the READONLY_VAR variable read-only, and attempting to modify its value resulted in an error.

Manage Environment Variables with the set Command

In this step, you will learn how to manage environment variables using the set command.

Environment variables are a special type of shell variables that are accessible to all processes running in the system. They are often used to store configuration settings, paths, and other important information.

Let's start by displaying the current environment variables:

set -o | grep -E '^[a-Z_]+='

Example output:

BASH_COMPLETION_COMPAT_DIR=/etc/bash_completion.d
HISTCONTROL=ignoreboth
HISTFILE=/home/labex/.bash_history
HISTFILESIZE=2000
HISTSIZE=1000
HOME=/home/labex
HOSTNAME=8d5d8d1f0a3f
LANG=en_US.UTF-8
LESSCLOSE='/usr/bin/lesspipe %s %s'
LESSOPEN='| /usr/bin/lesspipe %s'
LOGNAME=labex
LS_COLORS='rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:mi=00:su=37;41:sg=30;43:ca=30;41:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01;31:*.arc=01;31:*.arj=01;31:*.taz=01;31:*.lha=01;31:*.lz4=01;31:*.lzh=01;31:*.lzma=01;31:*.tlz=01;31:*.txz=01;31:*.tzo=01;31:*.t7z=01;31:*.zip=01;31:*.z=01;31:*.dz=01;31:*.gz=01;31:*.lrz=01;31:*.lz=01;31:*.lzo=01;31:*.xz=01;31:*.zst=01;31:*.tzst=01;31:*.bz2=01;31:*.bz=01;31:*.tbz=01;31:*.tbz2=01;31:*.tz=01;31:*.deb=01;31:*.rpm=01;31:*.jar=01;31:*.war=01;31:*.ear=01;31:*.sar=01;31:*.rar=01;31:*.alz=01;31:*.ace=01;31:*.zoo=01;31:*.cpio=01;31:*.7z=01;31:*.rz=01;31:*.cab=01;31:*.wim=01;31:*.swm=01;31:*.dwm=01;31:*.esd=01;31:*.jpg=01;35:*.jpeg=01;35:*.mjpg=01;35:*.mjpeg=01;35:*.gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35:*.xbm=01;35:*.xpm=01;35:*.tif=01;35:*.tiff=01;35:*.png=01;35:*.svg=01;35:*.svgz=01;35:*.mng=01;35:*.pcx=01;35:*.mov=01;35:*.mpg=01;35:*.mpeg=01;35:*.m2v=01;35:*.mkv=01;35:*.webm=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*.mp4v=01;35:*.vob=01;35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35:*.flc=01;35:*.avi=01;35:*.fli=01;35:*.flv=01;35:*.gl=01;35:*.dl=01;35:*.xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.cgm=01;35:*.emf=01;35:*.ogv=01;35:*.ogx=01;35:*.aac=00;36:*.au=00;36:*.flac=00;36:*.m4a=00;36:*.mid=00;36:*.midi=00;36:*.mka=00;36:*.mp3=00;36:*.mpc=00;36:*.ogg=00;36:*.ra=00;36:*.wav=00;36:*.oga=00;36:*.opus=00;36:*.spx=00;36:*.xspf=00;36:'
MACHTYPE=x86_64-pc-linux-gnu
MAILCHECK=60
OLDPWD=/home/labex
OPTERR=1
OPTIND=1
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
PIPESTATUS=([0]="0")
PPID=1
PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '
PS2='> '
PS4='+ '
PWD=/home/labex/project
RANDOM=1836
SHELL=/bin/bash
SHELLOPTS=braceexpand:hashall:interactive-comments:progcomp
SHLVL=1
SSH_CLIENT='172.17.0.1 52390 22'
SSH_CONNECTION='172.17.0.1 52390 172.17.0.2 22'
SSH_TTY=/dev/pts/0
TERM=xterm-256color
UID=1000
USER=labex
XDG_DATA_DIRS=/usr/local/share:/usr/share:/var/lib/snapd/desktop
XDG_RUNTIME_DIR=/run/user/1000
XDG_SESSION_ID=1
_=/usr/bin/env

As you can see, the output includes a list of all the environment variables currently set in the system.

Now, let's create a new environment variable:

export MYENV_VAR="This is an environment variable"

To verify that the variable was created correctly, we can use the echo command:

echo $MYENV_VAR

Example output:

This is an environment variable

To make an environment variable read-only, you can use the readonly command:

readonly READONLY_ENV_VAR="This variable is read-only"
READONLY_ENV_VAR="New value"

Example output:

bash: READONLY_ENV_VAR: readonly variable

As you can see, attempting to modify the READONLY_ENV_VAR variable resulted in an error.

Summary

In this lab, you learned about the purpose and syntax of the set command in Linux. The set command is used to set, unset, and display shell variables and options. You explored the various options that can be used with the set command, such as -a, -e, -u, and -x, and how to display all the currently set shell variables by running the set command without any arguments.

You also learned how to manage environment variables with the set command, which allows you to modify shell variables and control their behavior within the shell environment.

Linux Commands Cheat Sheet