====== Bash & Git ======
In this lab session, you're supposed to learn the basics of bash and git. 

**Bash** is the standard shell in many Linux distributions. Despite the ancient feeling, some tasks which are very tedious to do on a GUI can be solved pretty quickly on the command line. Especially if a task is very repetitive, there is a high chance that there exists a command line tool which can solve it faster.

**Git** is a version control system. Version control systems are primarily used in software development to keep track of all changes made by the software developers to any file within the software project. It keeps a version history and allows you to revert changes made to a file and to restore deleted files. Therefore, git is also useful if you work on a set of files on your own, but you want to keep track of every change you make and you want to be able to go back to a previous version if you make a mistake.

===== Useful resources =====
  * [[https://learncodethehardway.org/unix/bash_cheat_sheet.pdf|Bash Cheat sheet]]
  * [[https://wiki.ubuntuusers.de/Shell/Befehls%C3%BCbersicht/|List of common shell commands]] (in German)
  * [[https://rogerdudler.github.io/git-guide/|Git - the simple guide]]
  * [[https://www.atlassian.com/git/tutorials/undoing-changes|Undoing changes with Git]]
  * Type ''man ''  (note the space), followed by the name of a command, to the command line.\\ **Example**: ''man rm''\\ You will then see a manual page for that specific command. You can leave this screen by pressing the ''q'' key.
  * Google
===== Exercise 1: Bash and Git basics =====
In this exercise, you will use the most basic commands of git and bash. Make yourself familiar with these tools before we start with the more interesting part in Exercise 2.

  - Clone the git repository ''<nowiki>ssh://git@10.0.0.1/opt/git/ti2fp</nowiki>'' into a folder called ''ti2fp''. The username is ''git'' and the password is ''ti2lab''. (You will have to install git first.)
  - Create a new folder with the name of your nethz account.
  - Navigate into this folder and create a new git repository.
  - Copy the files and subfolders from the ''ti2fp'' folder into this folder.
  - Add these files to the git Index and commit them.
  - If you have worked with the command line before, you can skip the rest of this exercise and proceed to Exercise 2. 
  - We strongly recommend that, in the following exercises, you commit your changes every time you solve an exercise. This will allow you to undo any mistakes that you make.
  - Create a new file called ''empty.txt''.
  - List all files in that folder.
  - Create a copy of the file ''empty.txt'' called ''still-empty.txt''.
  - Open the file ''empty.txt'' in the text editor called ''nano'', add some text and save the file.
  - Output the content of the file on the command line.
  - The file is not empty anymore, so let's rename it to ''text.txt''.
  - Delete the file ''still-empty.txt''.

===== Exercise 2: Extracting data from files =====
In this exercise, you will see some basic commands to read data from files. You can save the output of a program to a file by using [[http://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO-3.html|redirects]].

  - Navigate into the ''csv-files'' folder. There, you will find a number of ''.csv'' files which contain stock prices of different stocks.
  - Print the content of ''msft.csv'' on the terminal. 
  - Create a file called ''allTheData.csv'' that contains every line from every ''*.csv'' file in the main folder. 
  - Count the number of lines in all ''.csv'' files and write them into the file ''numberOfLines.txt''.
  - You want to have a quick look at the data format in your ''.csv'' files. Write the first 10 lines of every ''.csv'' file into the file ''firstLines.txt''.
  - Your friend is interested in the latest stock prices. Write the last 20 lines of every ''.csv'' file into the file ''latestData.txt''.
  - Write the first three columns (Date, Open, High) of ''msft.csv'' into ''msft2.csv''.
===== Exercise 3: Searching, pipes and xargs =====
In the previous exercise, all tasks could be solved with just one command by passing some parameters to this command. In this exercise, we will learn how to search for files by their name and their content. Moreover, you are supposed to use [[http://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO-4.html|Pipes]] and (sometimes) the ''xargs'' command to pass on the output of one command to another command.

Go to the ''sourcecode'' folder. There, you will find hundreds of Java files in different subfolders. It would be tedious to open them all in a text editor if you were looking for something, wouldn't it?

  - Write the name of every ''.java'' file (including the path to the files starting from the folder ''sourcecode'') into a file called ''javaFilesList.txt''.
  - Print every line that contains the string ''author'' or ''Author''. 
  - List the name of every file that does not contain the string ''java'' in its filename. Write the output into the file ''otherFilesList.txt''.
  - Print the filename of every file that contains the string ''%%//%% Author: University of Zurich''. 
  - Delete those files. 
  - Commit your changes. Make sure that git also commits the removal of those files.
  - Go to the folder ''sourcecode/utils''. Print every file in this folder that does not contain ''DO NOT DELETE''. 
  - Delete those files. 
  - You realize that you did not want to delete these files. Use Git to restore the files that you removed in Exercise 8.
  - Use Git to restore the files that you removed in exercise 5.
  - The file ''allSrc.txt'' (in the folder ''sourcecode'') contains a list of files. Write every line of these files that contain the word ''static'' into the file ''static.txt''. 

===== Exercise 4: sed and Git branches =====
**sed** is a very powerful tool to edit text files on the command line. It is often used for search-and-replace operations. As you will see shortly, you can do a simple search-and-replace operation or delete a couple of lines - all of this can be done in many files at once.

You will also see **[[https://git-scm.com/book/en/v2/Git-Branching-Branches-in-a-Nutshell|Git Branches]]** in this exercise.

  - Create a git branch called ''experimental''.
  - Check out your newly created branch.
  - Go to the folder ''core''.
  - Replace the string ''%%// Author: University of Zurich%%'' with ''%%// Author: ETH Zurich%%'' in all files in this directory.
  - Navigate to the ''csv-files'' directory. Remove every odd line from every csv file in this folder.
  - Go back to the Git ''master'' branch.
===== Exercise 5: Bash scripting =====
In this exercise we advise you to write bash scripts, i.e., *.sh files. They will make life a bit easier. You can find some basic information [[http://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO-5.html|here]] and [[http://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO-6.html|here]].
  - You work together with a colleague who uses Windows. Thus, he cannot checkout the repository (because the files in the folder ''files with dots'' contain a '':'').  Replace all the '':'' with ''_''. 
  - Write a script that prints out ''is running'' if ''looper'' is running and ''is not running'' otherwise. Note that this process is currently not running.
  - Update your script such that it starts ''looper'' if it is not running.
  - Update your script such that it continuously monitors ''looper''.
  - Update your script such that it accepts the names of several programs as parameter, i.e., ''./yourScript.sh looper backGround'' should work.