archive/ctk_archive/console_toolkit/source/exercises/TheAlternativeCourse.cls

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+

archive/ctk_archive/console_toolkit/source/exercises/exercises.tex

+\documentclass{TheAlternativeCourse}
+
+\usepackage{menukeys}
+\usepackage{tabularx}
+\usepackage{float}
+\usepackage{caption}
+
+\title{Console Toolkit Exercises}
+\date{}
+\author{}
+
+\begin{document}
+\maketitle
+
+\setlength{\parindent}{0cm}
+\setlength{\parskip}{12pt}
+
+\section{Introduction}
+
+Welcome to this exercise session! This is a practical exercise on the Linux
+command line.  If you have any question about the exercises, feel free to ask
+the helpers for assistance.
+
+\subsection*{Difficulty}
+
+The exercises are designed in such a way that you will have to find solutions
+by reading the manuals and using search engines. You are expected to come up
+with appropriate solutions on your own, there will be no step-by-step guided
+exercises!
+
+There will be quite simple exercises for complete beginners at the start,
+but there are also some much more difficult ones further into the exercise.
+Feel free to skip ahead!
+
+\subsection*{Liability}
+
+By taking part in this exercise, you acknowledge that you alone are responsible
+for your computer. TheAlternative and its parent organisation, the Student
+Sustainability Commission, will not be held liable for any damages or loss of
+data.
+
+\pagebreak
+
+\section{Basics}
+
+To solve some of the exercises, you will need to download some files. Whenever
+you see an orange box like below, this means you have a task to solve.
+
+\begin{exercisebox}{Getting the repository}
+    Open a terminal and enter the following (all on one line): \\
+    \texttt{curl https://files.project21.ch/LinuxDays-Public/HS18-exercise.zip
+        -o exercises.zip} \\\\
+    Then extract the zip archive like this: \\
+    \texttt{unzip exercises.zip}
+\end{exercisebox}
+
+\subsection{Running a command}
+
+To run a command, you just type it into the console and hit enter.  Most useful
+commands require some arguments. Arguments are given after the name of the
+command, separated by spaces. There are also so-called \emph{flags}, which set
+some options to alter the behaviour of a command. They have the form
+\texttt{-x} (single letter form) or \texttt{--long-option} (long format).
+
+An example of a more involved command:
+
+\begin{cmdbox}
+\texttt{ls -l --human-readable \textasciitilde/Downloads}
+\end{cmdbox}
+
+\subsection{Getting help}
+
+\texttt{man} is a command you will need throughout the following
+exercises.  It stands for ``manual'' and shows you what almost any given
+command can do and which options are available for it.  Almost all commands
+provide such a ``manpage'', which is typically written by the developers
+themselves.
+
+\begin{exercisebox}{The manual's manual}
+    The \texttt{man} command itself has its own manpage. Type \texttt{man man}
+    to access it, use the arrow keys to scroll, and press \keys{q} to exit.
+    Have a look around, especially at the different section numbers.
+    What is the section number for system calls?
+\end{exercisebox}
+
+An alternative to using the man pages is to try and see if a command has a help
+option. This is usually displayed by appending the option \texttt{--help} after
+the name of the command, which will often display much shorter and concise
+instructions
+on how to use a command.
+
+\begin{exercisebox}{The help option}
+    Look at the help output of \texttt{ls}. What is the flag to see hidden
+    files?
+\end{exercisebox}
+
+\subsection{Navigating directories}
+
+You can navigate your file system in the terminal, just like you could with
+a graphical program. Below are the most important commands.
+
+\begin{table}[H]
+    \centering
+    \rowcolors{1}{lightblue}{white}
+    \begin{tcolorbox}[%
+        enhanced,
+        width=1.0\linewidth,
+        fuzzy shadow={1mm}{-1mm}{0mm}{0.1mm}{black!50!white},
+        tabularx={>{\centering\arraybackslash}l|>{\centering\arraybackslash}X},
+        title={Commands for navigating directories}]
+        \textbf{Command} & \textbf{Description} \\
+        \texttt{pwd} & Display the current working directory. \\
+        \texttt{tree DIR} & Get a visualization of the directory tree under
+	    \texttt{DIR}. \\
+        \texttt{ls DIR} & List all files and directories in the current
+            working directory. \\
+        \texttt{cd DIR} & Change the current working directory to the given
+            directory. \\
+    \end{tcolorbox}%
+    \label{tab1}
+\end{table}
+
+\begin{exercisebox}{Making yourself at home}
+    Have a look around your home directory and try out the mentioned commands.
+    You will most likely recognise the layout from your graphical file browser.
+    Remember you can always return to your home directory by running
+    \texttt{cd} without any arguments.
+\end{exercisebox}
+
+\subsection{Modifying directories}
+
+Just like in graphical programs, you can create and delete directories on the
+command line.
+
+\begin{table}[H]
+    \centering
+    \rowcolors{1}{lightblue}{white}
+    \begin{tcolorbox}[%
+        enhanced,
+        fuzzy shadow={1mm}{-1mm}{0mm}{0.1mm}{black!50!white},
+        width=1.0\linewidth,
+        tabularx={>{\centering\arraybackslash}l|>{\centering\arraybackslash}X},
+        title={Commands for modifying directories}]
+        \textbf{Command} & \textbf{Description} \\
+        \texttt{mkdir DIR} & Create a new directory with the given name. \\
+        \texttt{rmdir DIR} & Remove a directory. Will not work with
+            non-empty directories. \\
+        \texttt{rm -r DIR} &  Remove a directory and its contents.
+            {\color{exclamred}Attention! There is no trashcan on the command
+            line!  Files and directories will be deleted irrevocably.} \\
+        \texttt{cp -r SOURCE TARGET} &  Copy a source directory
+            (recursively with all its contents) to a target. \\
+        \texttt{mv SOURCE TARGET} & Move a file or directory.
+            Also used to rename files/directories. \\
+    \end{tcolorbox}%
+    \label{tab2}
+\end{table}
+
+\begin{exercisebox}{Creating your first directory}
+    Create a directory for the following exercises (you can call it
+    \texttt{console-toolkit}). Change into that directory and create a file
+    called \texttt{notes}. Then move the exercise file directory you downloaded
+    in task 2.1 into your newly created directory.
+\end{exercisebox}
+
+\subsection{Viewing files}
+If you want to view the contents of a text file, you have the following
+options:
+
+\begin{table}[H]
+    \centering
+    \rowcolors{1}{lightblue}{white}
+    \begin{tcolorbox}[%
+        enhanced,
+        fuzzy shadow={1mm}{-1mm}{0mm}{0.1mm}{black!50!white},
+        width=1.0\linewidth,
+        tabularx={>{\centering\arraybackslash}l|>{\centering\arraybackslash}X},
+        title={Commands for viewing files}]
+        \textbf{Command} & \textbf{Description} \\
+        \texttt{cat FILE} & Output a file to the terminal. \\
+        \texttt{head FILE} & Output the first couple of lines to the terminal. \\
+        \texttt{tail FILE} & Output the last couple of lines to the terminal. \\
+        \texttt{less FILE} & Browse a file in a visual viewer. \\
+    \end{tcolorbox}%
+    \label{tab3}
+\end{table}
+
+\begin{exercisebox}{Log files}
+    \texttt{tail} is often used to inspect errors log files. Use tail to find the
+    last three lines of \texttt{dmesg\_log} (in the exercise files).
+\end{exercisebox}
+
+\hintbox{\texttt{dmesg} is tool to view the log output of your kernel.}
+
+\subsection{Console tips \& tricks}
+
+There are many small things that can make your life when using the terminal
+little bit easier.  Following is a table with the most important keyboard
+shortcuts you can use to speed up your workflow.
+
+\begin{table}[H]
+    \centering
+    \rowcolors{1}{lightblue}{white}
+    \begin{tcolorbox}[%
+        enhanced,
+        fuzzy shadow={1mm}{-1mm}{0mm}{0.1mm}{black!50!white},
+        width=1.0\linewidth,
+        tabularx={>{\centering\arraybackslash}l|>{\centering\arraybackslash}X},
+        title={Terminal keyboard shortcuts}]
+        \keys{\ctrl}+\keys{w} & Delete one word backwards. \\
+        \keys{\ctrl}+\keys{u} & Delete the entire line. \\
+        \keys{\ctrl}+\keys{l} & Clear the terminal. \\
+        \keys{\ctrl}+\keys{a} & Go to the beginning of the line. \\
+        \keys{\ctrl}+\keys{e} & Go to the end of the line. \\
+        \keys{\ctrl}+\keys{c} & Terminate the currently runnig process. \\
+        \keys{\ctrl}+\keys{d} & Quit the shell. \\
+    \end{tcolorbox}%
+    \label{tab4}
+\end{table}
+
+\section{Files \& Permissions}
+
+This section introduces you to basic commands related to files. We will first
+look at a command that can be used for creating empty files.
+
+The \texttt{touch} command is most frequently used for creating new, empty
+files. If you check the manual, you will see that it can also change certain
+file timestamps (access and modification times).
+
+\begin{exercisebox}{The magic touch}
+    Switch to your home directory. Execute \texttt{touch file}. A new file
+    should have been created. Confirm that this is the case.
+\end{exercisebox}
+%
+We already saw \texttt{cat} in the previous section. Another tool to look at
+files is \texttt{less}. This command is great if you want to look at large
+bodies of text because unlike \texttt{cat}, it has a built-in scroll function.
+Once you are done looking at the file, you can quit with \keys{q}.
+
+\subsection{Permissions}
+
+We will now look at two commands to manage permissions.
+
+\texttt{chown} stands for ``change owner''. It is used to change the owner of a
+given file. It can also change the group ownership.
+
+\begin{exercisebox}{Get off my lawn}
+    Create a new, empty file (hint: \texttt{touch}) and use \texttt{chown} to
+    change its ownership to the \texttt{root} user (you will probably need
+    \texttt{sudo} for this). Try deleting it. Then change the ownership back to
+    your own user.
+\end{exercisebox}
+%
+A very similar command is \texttt{chmod}. \texttt{chmod} stands for ``change
+file mode bits'' and controls the following permissions on any given file:
+
+\begin{itemize}
+    \setlength\itemsep{-9pt}
+	\item Read: Who can see the file data.
+	\item Write: Who can modify the file.
+	\item Execute: Who is allowed to run the file (like a program or a script)
+\end{itemize}
+
+\hintbox{Permissions can be viewed using \texttt{ls -l}.}
+
+\begin{exercisebox}{{Read, Write, Execute}}
+    The read, write and execute permissions do different things, depending on
+    whether they are set for directories or for files. Find out what they mean
+    for files and directorues by playing around with the \texttt{chmod}
+    command, readings its manual or searching on the internet.
+\end{exercisebox}
+
+\subsection{File tools}
+
+There are a number of other commands that are frequently used to get
+information on files:
+
+\begin{table}[H]
+    \centering
+    \rowcolors{1}{lightblue}{white}
+    \begin{tcolorbox}[%
+        enhanced,
+        fuzzy shadow={1mm}{-1mm}{0mm}{0.1mm}{black!50!white},
+        width=1.0\linewidth,
+        tabularx={>{\centering\arraybackslash}l|>{\centering\arraybackslash}X},
+        title={Commands for getting information about files}]
+        \textbf{Command} & \textbf{Description} \\
+	    \texttt{wc \$file} & Display line, word, and character count of a file \\
+        \texttt{diff \$file1 \$file2} & Show differences between files \\
+	    \texttt{ln \$target \$link\_name} & Create a link \\
+        \texttt{du \$file} & Estimate file space usage \\
+        \texttt{df} & Report file system disk usage \\
+    \end{tcolorbox}%
+    \label{tab5}
+\end{table}
+
+In the next exercise we are going to read some text from the standard input
+(also called \texttt{stdin}). Reading from \texttt{stdin} means you can just
+type text into the console. When you are done, hit \keys{Enter} to enter a
+newline and then hit \keys{\ctrl}+\keys{d}. This is the universal end-of-file
+character in Unix-like systems. It signals to the command that it the input has
+finished. You can even use this key shortcut to close your terminal.
+
+\begin{exercisebox}{Cat tricks}
+    Type the command \texttt{cat -}. This starts \texttt{cat} to read from
+    \texttt{stdin}. Enter some text and observe what happens when you press
+    \keys{Enter}. \texttt{cat} will just keep reading until the end-of-file
+    character, so you can enter multiple lines of text. When you are done,
+    terminate the input as described above.
+\end{exercisebox}
+
+\begin{exercisebox}{Counting words}
+    Sometimes you might want to know the length of some text. First, consult
+    \texttt{wc}'s manual to find out how you can read from standard input. Copy
+    a line of text of your choice from the \texttt{wc} manual, then use the
+    \texttt{wc} syntax that you looked up to read from standard input. Paste
+    the text and terminate the input as before.
+\end{exercisebox}
+
+\hintbox{%
+Copying and pasting in the console usually works with
+\keys{\ctrl}+\keys{\shift}+\keys{c} and \keys{\ctrl}+\keys{\shift}+\keys{v},
+this depends on the terminal though.}
+
+\paragraph{Hardlink}
+A hardlink is a pointer to a specific, physical location on a hard disk. If the
+file name of the file that is linked to changes, the link still works. However,
+if the file is replaced by a different file with the same name, the hardlink
+will now \emph{not} point to the new file!  It will still point to the location
+of the old file.
+
+\paragraph{Symlink}
+A symlink (short for symbolic link) points to a file name, to an actual file
+path. If the data behind the file name is changed, the symbolic link will then
+point to this new file, as long as the name stays the same. This is a higher
+level concept than a hardlink, as it operates above the concept of file names.
+Most of the time, a symlink is preferrable to a hardlink.
+
+\begin{exercisebox}{Symlinks}
+    Have a look at the \texttt{ln} manual to find out how to create a symbolic
+    link. Then create a link in your home directory to a directory you use
+    frequently.
+\end{exercisebox}
+
+Lastly, two commands that are loosely related to files are \texttt{df} and
+\texttt{du}. These commands are used to find out how much space files take up.
+\texttt{df} shows coarse-grained disk usage as reported by the file system.
+\texttt{du} counts the disk usage of individual files and directories.
+
+\begin{exercisebox}{Reporting disk usage}
+    When you run \texttt{df} and \texttt{du}, the sizes of files are reported
+    in multiples of blocks. The size of a block depends on your file system,
+    but typically is between 512 bytes and 1 kilobyte. This means that you
+    would have to multiply by this size the true size, in bytes. Find out how
+    to make the output of \texttt{df} and \texttt{du} more readable for humans
+    by looking at their options in the manual (hint: the option is the same for
+    both tools).
+\end{exercisebox}
+
+\section{Leveraging the command line}
+
+\subsection{Globbing (Wildcards)}
+
+Globbing is a useful tool to work with files that share a pattern. For example,
+to refer to all \texttt{jpg} images in a directory, you can use \texttt{*.jpg}.
+The \texttt{*} means `any number of any characters', so this pattern will give
+you all files that end with \texttt{.jpg}. Similarly, \texttt{dir/*} will give
+you \emph{all} files in \texttt{dir}, \emph{except} hidden files.
+
+There are a few more useful patterns, like \texttt{?} (question mark) which
+matches any \emph{single} character, or \texttt{\string{*.jpg,*.png\string}},
+which is a list that matches both \texttt{.jpg} and \texttt{.png} files. To
+learn more, you can have a look at \texttt{man 7 glob}.
+
+\begin{exercisebox}{{Printing text, again}}
+    Ouput all \texttt{.txt} files in \texttt{notes/} to the terminal in
+    a single command. The output will tell you if you did it correctly.
+\end{exercisebox}
+
+\begin{exercisebox}{Managing cat pictures}
+    Create a new directory called \texttt{cats}. Copy all cat pictures in
+    \texttt{pictures/} (in the exercise files) to your new \texttt{cats}
+    directory, with a single command.
+\end{exercisebox}
+
+\subsection{Pipes}
+
+Pipes are useful to connect multiple commands together. One of the design
+principles of Unix was ``do one thing, and do it well''. This means, tools
+should be simple and powerful in their specific domain, but there should also
+be a mechanism to combine multiple programs in an easy way. This mechanism is
+the \emph{pipe}, the \texttt{|} symbol. It allows you to connect the output of
+one program to the input of another program.
+
+For example, we can combine \texttt{du} and \texttt{sort} to work together.
+\texttt{du} analyses the usage of disk space, and sort just sorts lines
+it is given. This pipe analyzes your home directory and tells you which
+directory uses the most space:
+
+\begin{cmdbox}
+    \texttt{du -sh * | sort -h}
+\end{cmdbox}
+
+Here the \texttt{*} globbing pattern stands for ``every file in the current
+directory''.
+
+\begin{exercisebox}{Counting lines in multiple files}
+    \texttt{wc} (word count) can be used to count the number of lines in a file
+    (\texttt{-l} flag). Use \texttt{cat} to output all files in the
+    \texttt{notes} directory (exercise files) at the same time and connect it
+    to \texttt{wc} to count the lines.
+\end{exercisebox}
+
+\subsection{Find}
+
+Looking for specific files on your system is a task that one has to do fairly
+regularly. Two very popular tool for finding files with certain properties are
+\texttt{find} and \texttt{grep}. In this section, we cover \texttt{find}.  As a
+rule of thumb, \texttt{find} is best used when you know that your file has
+certain metadata: Maybe you know approximately when you have created the file,
+when you last looked at it, how large it is etc. In contrast, \texttt{grep} is
+usually used when you want to look at \emph{the content} of a file.
+
+\texttt{find} works by essentially filtering all files through a chain of
+conditions, given by flags. Working with \texttt{find} is
+fairly straight forward and almost like verbally explaining what you are
+looking for.
+
+\begin{cmdbox}
+    \texttt{find -mtime -1 -size +100k}
+\end{cmdbox}
+
+This searches for all files that have been modified (\texttt{-mtime}) less than
+one day ago (\texttt{-1}) and have size (\texttt{-size}) larger than 100
+Kilobytes (\texttt{+100k}). \texttt{find} has a lot of conditions where it
+makes sense to specify ``greater than'' or ``smaller than''. This is specified
+by prefixing the amount with a \texttt{+} or a \texttt{-}. This is why the
+condition ``larger than 100 Kilobytes'' is written as \texttt{-size +100k}.
+
+If we additionally knew that our file was smaller than one gigabyte, we would
+type:
+\begin{cmdbox}
+    \texttt{find -mtime -1 -size +100k -size -2G}
+\end{cmdbox}
+
+It's necessary to use \texttt{-2G} here, since file sizes are rounded up.
+A file that has 800M will be rounded to 1G. The semantics of find use strictly
+smaller (\texttt{<}), therefore we have to compare to 2G.
+
+Here is an overview of options for \texttt{find} that are useful to know.
+
+\begin{table}[H]
+    \centering
+    \rowcolors{1}{lightblue}{white}
+    \begin{tcolorbox}[%
+        enhanced,
+        fuzzy shadow={1mm}{-1mm}{0mm}{0.1mm}{black!50!white},
+        width=1.0\linewidth,
+        tabularx={>{\centering\arraybackslash}l|>{\centering\arraybackslash}X},
+        title={Useful find flags}]
+        \textbf{Flag} & \textbf{Description} \\
+        \texttt{-name} & Matches the name of a file. \\
+	    \texttt{-size} & Condition on the size of a file. \\
+        \texttt{-atime} & Condition on when file was last accessed. \\
+        \texttt{-mtime} & Condition on when file was last modified. \\
+        \texttt{-type} & Specifies type of file (directory, regular file
+        \ldots). \\
+    \end{tcolorbox}%
+    \label{tab6}
+\end{table}
+
+\begin{exercisebox}{The largest cat}
+    Use \texttt{find} to find all cat pictures (\texttt{cat*}) with a size over
+    200 kilobytes in the exercise directory. There should be more than one!
+\end{exercisebox}
+
+\subsection{Grep and regular expressions}
+
+\includegraphics[width=\textwidth]{img/regex_golf.png}
+{\footnotesize xkcd 1313, https://xkcd.com/1313/}
+
+While working with many files in different folders, you can find yourself
+losing track of what is in what file. To quickly find something in one of many
+files, you can use \texttt{grep}. Grep is a tool for searching a body of text
+for a specific pattern. Those patterns are specified with a syntax called
+``Regular Expressions'' or regexes.
+
+Regexes can easily become \emph{very} complicated (there are entire books on
+this topic).  We'll have a look at the very basics here. Regexes are comprised
+of a string of characters, e.g. \texttt{foo.bar[0-9]}. Let's look at it in more
+detail:
+
+\begin{itemize}
+    \setlength\itemsep{-9pt}
+    \item{\makebox[1.5cm]{\: \texttt{foo\hfill}} Matches the literal word ``foo''.}
+    \item{\makebox[1.5cm]{\: \texttt{.\hfill}} Matches any single character.}
+    \item{\makebox[1.5cm]{\: \texttt{bar\hfill}} Matches the literal word ``bar''.}
+    \item{\makebox[1.5cm]{\: \texttt{[0-9]\hfill}} Matches a single digit between 0 and 9.}
+\end{itemize}
+
+For example, this regex \texttt{foo.bar[0-9]} would match on all of these
+strings:
+
+\begin{itemize}
+    \setlength\itemsep{-9pt}
+    \item \texttt{foo\_bar1}
+    \item \texttt{fooobar9}
+    \item \texttt{foozbar5}
+    \item \texttt{foo1bar2}
+\end{itemize}
+
+An important thing to note is that regular expressions don't have to match the
+entire string. So the example regex would also match on
+\texttt{XXXXfoo1bar2XXXX}, because \texttt{foo1bar2} is part of that string.
+
+So how do we try that on the command line? Simple, to test out \texttt{grep},
+we can use \texttt{echo} to pipe a string into grep to match. Like this:
+
+\begin{cmdbox}
+    \texttt{echo foo1bar2 | grep foo.bar[0-9]}
+\end{cmdbox}
+
+This should output \texttt{foo1bar2}, because grep outputs all lines from its
+input that match the regex.
+
+There are a few command line options that you should know about \texttt{grep}.
+These can also be combined, like so: \texttt{grep -rnoh PATTERN FILE}.
+
+\begin{table}[H]
+    \centering
+    \rowcolors{1}{lightblue}{white}
+    \begin{tcolorbox}[%
+        enhanced,
+        fuzzy shadow={1mm}{-1mm}{0mm}{0.1mm}{black!50!white},
+        width=1.0\linewidth,
+        tabularx={>{\centering\arraybackslash}l|>{\centering\arraybackslash}X},
+        title={Useful grep flags}]
+        \textbf{Command} & \textbf{Description} \\
+        \texttt{-r} & Recursively look at all files under the given directory. \\
+        \texttt{-o} & Only print the matching strings, not the entire line. \\
+        \texttt{-h} & Don't print the filename, just the matching string/line. \\
+        \texttt{-n} & Prefix the output with the linenumber where the match occured. \\
+    \end{tcolorbox}%
+    \label{tabgrepopts}
+\end{table}
+
+\begin{table}[H]
+    \centering
+    \rowcolors{1}{lightblue}{white}
+    \begin{tcolorbox}[%
+        enhanced,
+        fuzzy shadow={1mm}{-1mm}{0mm}{0.1mm}{black!50!white},
+        width=1.0\linewidth,
+        tabularx={>{\centering\arraybackslash}l|>{\centering\arraybackslash}l|>{\centering\arraybackslash}X},
+        title={Regex building blocks}]
+        \textbf{Regex} & \textbf{Example} & \textbf{Description} \\
+
+		\textbf{Match Expressions} & & \\
+        \texttt{<character literal>} & \texttt{f} &
+            Matches the character \texttt{<character literal>}.
+            The example matches on \texttt{f}. \\
+        \texttt{.} & \texttt{.} & Matches any single character. \\
+        \texttt{[<char1>-<char2>]} & \texttt{[a-z]} &
+            Matches a single character in the range from \texttt{<char1>} to
+            \texttt{<char2>} (inclusive). The example matches on any lowercase
+            character. The character range can be specified multiple times,
+            like so: \texttt{[a-zA-Z0-9]}. This would match any lower- or
+            uppercase character or digit. \\
+        \texttt{[[:alnum:]]} & \texttt{[[:alnum:]]} &
+            Alphanumeric characters (letters and digits). \\
+        \texttt{[[:alpha:]]} & \texttt{[[:alpha:]]} & Letters. \\
+        \texttt{[[:digit:]]} & \texttt{[[:digit:]]} & Digits. \\
+        \texttt{[[:xdigit:]]} & \texttt{[[:xdigit:]]} & Hexadecimal digits. \\
+        \texttt{[[:blank:]]} & \texttt{[[:blank:]]} & Blank space (spaces and tabs). \\
+        \texttt{[[:word:]]} & \texttt{[[:word:]]} & Digits, letters and underscores. \\
+
+		\textbf{Modifiers} & & \\
+        \texttt{?} & \texttt{.?} &
+            The preceding expression appears zero times or exactly once. The
+            example would match on an empty string or any string of length one. \\
+        \texttt{*} & \texttt{.*} &
+            The preceding expression appears zero, one or many times. The
+            example would match on a string of arbitrary length, including an
+            empty one.\\
+        \texttt{+} & \texttt{.+} &
+            The preceding expression appears one or many times. The example
+            matches on a string of any length greater than zero. \\
+        \texttt{\string{<num>\string}} & \texttt{\string{3\string}} &
+            Matches on a string if the preceding expression appears exactly
+            \texttt{<num>} times. \\
+        \texttt{\string{<num1>,<num2>\string}} & \texttt{\string{3,6\string}} &
+            Matches on a string if the preceding expression appears between
+            \texttt{<num1>} and \texttt{<num2>} times (inclusive). \\
+    \end{tcolorbox}%
+    \label{tabgreplarge}
+\end{table}
+
+\paragraph{Note} When using the characters \texttt{|, +, ?} with their regex
+meaning, they must be escaped with a backslash like this: \verb@\|, \+, \?@. If
+you want to use any of the ofter special characters as regular characters, i.e.
+to match a literal \texttt{.} you can use \verb@\.@
+
+\begin{exercisebox}{Finding email addresses}
+    Somewhere in the exercise files, there is an email address hidden in a text
+    file. Create a regular expression that matches email addresses that end in
+    .ch and find it!
+\end{exercisebox}
+
+\section{Remote machines}
+
+This section will be about working with remote machines. You will
+connect to one and move files from and to it. Additionally, you will set up
+your SSH so you can log in without entering a password.
+
+\texttt{ssh} (secure shell) is an extremely useful tool, as it allows you to
+manage servers, connecting to your home computer from a laptop, running
+computations on super computers, and even using graphical applications that are
+installed on a different computer. \texttt{scp} (secure copy) works just like
+\texttt{cp}, but allows you to copy files to and from remote machines.
+\texttt{scp} is based on the SSH protocol, so it works similiarly and the
+public key authentication in exercise 5.2 will automatically also apply to
+\texttt{scp}.
+
+\begin{table}[H]
+    \centering
+    \rowcolors{1}{lightblue}{white}
+    \begin{tcolorbox}[%
+        enhanced,
+        fuzzy shadow={1mm}{-1mm}{0mm}{0.1mm}{black!50!white},
+        width=1.0\linewidth,
+        tabularx={>{\centering\arraybackslash}l|>{\centering\arraybackslash}X},
+        title={Remote access tools}]
+        \texttt{ssh user@hostname} &
+            Open an SSH session with a specific user on a host. \\
+        \texttt{scp user@hostname:file.txt .} &
+            Copy a file from remote machine to the current directory. \\
+        \texttt{scp file.txt user@hostname:file.txt} &
+            Copy a file from current directory to remote host. \\
+    \end{tcolorbox}%
+    \label{tab7}
+\end{table}
+
+\hintbox{%
+If you don't have an ETH account, use\\
+\texttt{hackingsession@pterodactyl.vsos.ethz.ch} with password\\
+\texttt{BoredHacker} for the following exercises instead.}
+
+\begin{exercisebox}{Establishing an SSH connection}
+    Use SSH to connect to the Euler supercomputer at
+    \texttt{nethz-login@euler.ethz.ch}, where \texttt{nethz-login} is your
+    \emph{nethz} account name. You can login using your regular credentials.
+\end{exercisebox}
+%
+It is inconvenient that you have to enter your password every time you want to
+log in. You can set up SSH in a way where you \emph{don't} have to provide your
+password!  This is done with public key cryptography. Basically, you generate a
+public key and a private key.  The private key you keep safe and only for
+yourself. The public key you can distribute to anyone.  Now you can
+authenticate yourself for anyone that has your public key: You can create a
+signature with your private key, that can be verified using the public key.
+However, only the owner of the private key can create the signature that is
+verifiable by the public key! This can be used by an SSH server to authenticate
+clients that want to open an SSH session.
+
+\begin{exercisebox}{Generating your key}
+    Generate your private/public key pair using \texttt{ssh-keygen}.
+    Then copy your generated public key (\texttt{.ssh/id\_rsa.pub}) to
+    \texttt{.ssh/authorized\_keys} on the server. Try logging in with SSH now,
+    it should no longer require a password.
+\end{exercisebox}
+
+
+\section{Jobs \& Processes}
+
+Jobs are groups of processes that are running in the current shell. Often, a
+job only consists of one process but sometimes a job is a process
+\emph{pipeline} consisting of multiple jobs, such as
+\texttt{echo "Hello" | cat -}. Consult the \texttt{JOB CONTROL} section
+of the \texttt{bash} manual if you want to study the details.
+
+Knowing how to control jobs is essential if you want to be able to
+simultaneously run multiple processes from the same shell.
+
+\subsection{Job control}
+
+Jobs can be put into the background, started in the background, brought to the
+foreground and killed. We say a job is running in the background when it is
+currently running, but not blocking the shell. In other words, when a job is
+running in the background, you can still use your shell normally (although the
+job might produce output that will get displayed on your terminal which can be
+quite annoying).
+
+\begin{table}[H]
+    \centering
+    \rowcolors{1}{lightblue}{white}
+    \begin{tcolorbox}[%
+        enhanced,
+        fuzzy shadow={1mm}{-1mm}{0mm}{0.1mm}{black!50!white},
+        width=1.0\linewidth,
+        tabularx={>{\centering\arraybackslash}l|>{\centering\arraybackslash}X},
+        title={Working with jobs}]
+	    \texttt{jobs} & List all jobs in the current shell\\
+	    \texttt{cmd \&} & Start \texttt{cmd} in the background\\
+	    \texttt{fg} & Bring a job into the foreground\\
+	    \texttt{bg} & Bring a job into the background\\
+    \end{tcolorbox}
+    \label{tabjobcmds}
+\end{table}
+
+\begin{table}[H]
+    \centering
+    \rowcolors{1}{lightblue}{white}
+    \begin{tcolorbox}[%
+        enhanced,
+        fuzzy shadow={1mm}{-1mm}{0mm}{0.1mm}{black!50!white},
+        width=1.0\linewidth,
+        tabularx={>{\centering\arraybackslash}l|>{\centering\arraybackslash}X},
+        title={Controlling jobs}]
+		\texttt{\keys{\ctrl}+\keys{z}} & Suspend current job. Processes may ignore this.\\
+		\texttt{\keys{\ctrl}+\keys{c}} & Kill current job. Processes may ignore this.\\
+        \texttt{kill \%N} & Kill job, where N is its number as listed in
+        \texttt{jobs}.Processes may \emph{still} ignore this.\\
+	    \texttt{kill -9 \%N} & Kill job with number N for sure.\\
+    \end{tcolorbox}
+    \label{tab8}
+\end{table}
+
+You can \emph{usually} use \keys{\ctrl}+\keys{c} to terminate a job in the
+foreground and \keys{\ctrl}+\keys{z} to suspend a job in the foreground.
+Suspended jobs are paused until they are resumed with either \texttt{fg} or
+\texttt{bg}. Note that processes can choose to overwrite these shortcuts so
+they are not guaranteed to work. If they don't work, we can always use more
+drastic measures \ldots
+
+\subsection{Processes}
+
+Processes operate system-wide. Each process has a unique process ID, called the
+PID for short. You can think of processes as separate programs running
+independent of each other. For example, an \texttt{echo} command spawns a new
+process that is separated from the shell process that you are in (which is
+typically \texttt{bash}).
+
+\begin{table}[H]
+    \centering
+    \rowcolors{1}{lightblue}{white}
+    \begin{tcolorbox}[%
+        enhanced,
+        fuzzy shadow={1mm}{-1mm}{0mm}{0.1mm}{black!50!white},
+        width=1.0\linewidth,
+        tabularx={>{\centering\arraybackslash}l|>{\centering\arraybackslash}X},
+        title={Managing}]
+        \texttt{top} & Display info about all currently running processes. Quit
+        with \keys{q}\\
+        \texttt{htop} & A more modern equivalent of \texttt{top}. It is not
+        installed by default on most distributions, but can be installed it
+        with your package manager. \\
+        \texttt{kill \texttt{PID}} & Send a termination signal to the process
+        \texttt{PID}. This is the preferred way to terminate a process, as it
+        allows it to exit normally and perform clean up. \\
+        \texttt{kill -9 \texttt{PID}} & Send a killing signal to the
+        process \texttt{PID}. The process is killed by the operating system
+        immediately. Useful for unresponsive processes. \\
+        \texttt{pkill \texttt{PATTERN}} & Like \texttt{kill}, but kills
+        processes whose names match a pattern instead. \\
+	    \texttt{pkill -9 \texttt{PATTERN}} & Send a kill signal instead. \\
+        \texttt{ps} & Utility to display information about processes. Most
+        commonly used as \texttt{ps aux}. \\
+    \end{tcolorbox}%
+    \label{tab9}
+\end{table}
+
+\texttt{kill} and \texttt{pkill} actually send so-called signals to processes.
+There are many signals that all do different things. When you call \texttt{kill
+PID}, the signal \texttt{15} is sent to the process \texttt{PID}. This signal
+is called the \texttt{SIGTERM} signal and is used to \emph{ask} a process to
+terminate. When we write \texttt{kill -9 PID}, we are actually sending the
+signal \texttt{9} which is also known as \texttt{SIGKILL} and kills a process
+instantly. Read \texttt{man 7 signal} if you want to know more about signals.
+
+
+\begin{exercisebox}{Killed in their sleep}
+    Start a new process by typing \texttt{sleep 1000} in your shell. Open
+    another shell. Use \texttt{top}, \texttt{htop} or \texttt{ps} to figure out
+    the PID of the \texttt{sleep} process. Kill it.
+\end{exercisebox}
+
+\begin{exercisebox}{A job for kill}
+    \texttt{kill} also works on jobs. Start \texttt{sleep 1000} in the
+    background (or start it in the foreground, suspend it, then bring it to the
+    background). Then type \texttt{kill \%N} where \texttt{N} is the job's number
+    (probably \texttt{1}). Check the output of the \texttt{jobs} command and
+    confirm that the job is not displayed anymore.
+\end{exercisebox}
+
+\section{License}
+
+This work is licensed under a Creative Commons Attribution-ShareAlike 4.0
+International License. See also:
+\url{http://creativecommons.org/licenses/by-sa/4.0/}.
+
+\vspace{0cm}
+\includegraphics[width=3cm]{assets/CC-BY-SA_icon.pdf}
+
+\end{document}

archive/ctk_archive/console_toolkit/source/slides/Makefile

+TEX=latexmk
+TEXOPTS=-output-directory=build \
+		-pdf \
+		-latexoption=-interaction=nonstopmode \
+		-latexoption=-file-line-error
+
+# set PREVIEW=1 to enable preview
+# example usage: make PREVIEW=1 target
+ifdef PREVIEW
+PREVIEWOPTS=-pvc
+endif
+
+default: pres
+
+# create build directory if it doesnt exist
+builddir:
+	@[ -d build ] || mkdir build
+
+pres: pres.tex builddir
+	@$(TEX) $(TEXOPTS) $(PREVIEWOPTS) $<
+	mv build/pres.pdf .
+
+clean:
+	@rm -rf build/*
+