Shell scripting and using the CLI

Mari Flåm

IT Avdelingen @ UiB��Contact at: �mari.flam@nerdschool.no

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Åse L Mattson

Developer @ Skatteetaten�

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https://www.meetup.com/bergen-nerdschool/

Workshop prerequisites

• A UNIX-like console�
• Linux or Mac? All set.�
• Windows? Git Bash or WSL

Intentions of this workshop

• Get a feel of using the terminal�
• Learn common shell commands�
• Create shell scripts to make your life easier

Why use the command line?

Why use the command line?

• Using the command line (or Command Line Interface - CLI) has many advantages and uses:
• Speed - The CLI is in many cases a lot faster than using a GUI if you know the commands
• Automation - Repetitive tasks can be automated using scripts
• Repeatability - Scripting tasks allow you to standardize how a task is performed, so that the result of the task is the same every time
• Power - The CLI is a very powerful tool that allows you to combine different commands to do a lot of work with little syntax
• Sometimes, you have no choice - When working on remote servers, you will probably not have access to a graphical user interface

CLI for programming

• A lot of tools for programming today are only accessible as command line programs, or much more efficient to use as command-line programs
• Learning to use the CLI will enable you to work more efficiently as a developer

The shell

How does the shell work?

• Type a command, press enter�
• Command executes immediately�
• Result is printed to the screen (standard output/standard out)

What is a command?

• Small program that you are able to execute from the command line�
• A command can take zero or many parameters / inputs ��
• Example:
• ls
• pwd
• cd

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General syntax for commands

• <command>
• <command> <argument>
• <command> -<parameter>
• <command> -<parameter> <argument>

Example:

• cp -R dir1/ dir2/ - copy all files and subdirectories from dir1 into dir2

Some “common” parameters�

• -h help
• -v version or verbose
• -r or -R recursive
• -n number
• -f file or force�
• Always check if you’re unsure. -h for Help is almost always available.

All PATHs lead to Rome

• The shell knows about the program (command) because it’s located in a directory the shell scans.�
• We can add and remove directories the shell should know about by modifying the machine’s PATH variable.

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• Pipe�
• Puts (pipes) commands together�
• Sends output from standard out (stdout) to standard in (stdin)
• (Output of one command becomes the input of the next command in the chain)

Assignments

Assignments outline�

• Exercise 1 - Getting started
• Exercise 2 - Basics of the shell
• Exercise 3 - Scripting
• Exercise 4 - Using pipelines and redirects
• Exercise 5 - Number guessing game

Assignments�

• Follow the README: https://github.com/nerdschoolbergen/shellscripting�
• Windows users: Git bash is a bash emulation layer. You may encounter some weirdness with i.e permissions�
• Use the solutions as hints if you like. You are here to learn, it is not an exam.�
• Try to type out stuff yourself to get a feel of using the terminal and its shortcuts

Contributing

• We are open source! �
• We appreciate any contribution, whether it be typos or suggestions for improvements (Create an issue in the issue tracker)

WIFI

• SSID: uib-guest
• Register with your phone number

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