public/subjects/devops/env-format/README.md

Env-format

Instructions

Create a script env-format.sh, which will print the environment variables that have the following formats:

• Print the PWD value.
• All the environment variables that have a letter H in the name, without printing the value of those variables.

$ printenv
SHELL=/bin/bash
QT_ACCESSIBILITY=1
NVM_RC_VERSION=
COLORTERM=truecolor
HOMEBREW_PREFIX=/home/linuxbrew/.linuxbrew
DESKTOP_SESSION=i3
...
PWD=/home/user
LOGNAME=user
MANPATH=/home/linuxbrew/.linuxbrew/share/man:
XDG_SESSION_DESKTOP=i3
XAUTHORITY=/run/user/1000/gdm/Xauthority
WINDOWPATH=2
SHELL=/bin/bash
SSH_AGENT_PID=2900
HOME=/home/user
HOMEBREW_SHELLENV_PREFIX=/home/linuxbrew/.linuxbrew
USERNAME=user
$

Expected output:

$ ./env-format.sh
/home/user/Documents/public/sh/tests/student
SHELL
SSH_AGENT_PID
HOMEBREW_SHELLENV_PREFIX
MANPATH
XAUTHORITY
WINDOWPATH
HOME
$

Hints

Environment variables are variables that contain values necessary to set up a shell environment. Contrary to shell variables, environment variables persist in the shell’s child processes.

VARIABLE_NAME=value

Most Common Environment Variables:

• PWD – Current working directory.
• HOME – The user’s home directory location.
• SHELL – Current shell (bash, zsh, etc.).
• LOGNAME – Name of the user.
• UID – User’s unique identifier.
• HOSTNAME – Device’s hostname on the network.
• MAIL – User’s mail directory.
• EDITOR – The Linux system default text editor.
• TEMP – Directory location for temporary files.

How to Check Environment Variables:

Structurally, environment and shell variables are the same – both are a key-value pair, separated by an equal sign.

• printenv. Prints the values of all or some environment variables.

$ printenv HOME
/home/user

Search Specific Environment Variables:

To find all the variables containing a certain character or pattern, use the grep command:

$ printenv | grep "W"
HOMEBREW_PREFIX=/home/linuxbrew/.linuxbrew
HOMEBREW_SHELLENV_PREFIX=/home/linuxbrew/.linuxbrew
PWD=/home/user/Documents/
WINDOWPATH=2
OLDPWD=/home/user/Public

• awk. The awk command is a Linux tool and programming language that allows users to process and manipulate data and produce formatted reports.

This flag will come in handy:

-F [separator] Used to specify a file separator. The default separator is a blank space.

$ cat example.txt
Hello:my:name:is:John
$ awk -F ":" '{print $5}' example.txt
John
$

You have to use Man or Google to know more about commands flags, in order to solve this exercise! Google and Man will be your friends!

References

• printenv.
• grep.
• awk