Linux Basics, Shell Scripting (2021-03-29)

Agenda

  • Day 1

    • Linux and UNIX concepts

    • Commandline: using the shell efficiently

    • Filesystem and permissions

  • Day 2

    • Tools: cat, cut, head, tail, grep, and the like

    • The pipe

    • Exercises: combine things to solve problems

  • Day 3

    • Shell scripting: Variables

    • Control flow: if, while

    • Exercises

  • Day 4

    • Functions

    • Subshells

    • Parameter expansion, here-documents, and more details

    • Exercises

Course Preparation

We will be using a Linux machine somewhere in the cloud, IP address 34.107.39.200. Please verify that you are able to login as follows (substitute my username with yours),

  • From a Linux system, use the ssh program (substitute my username with yours)

    $ ssh faschingbauer.joerg@34.107.39.200
The authenticity of host '34.107.39.200 (34.107.39.200)' can't be established.
ECDSA key fingerprint is SHA256:/in22o4VCD400X0bb4FlCb5/vQnrvKvOirgfqq6maPo.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '34.107.39.200' (ECDSA) to the list of known hosts.
faschingbauer.joerg@34.107.39.200's password:
Linux fh-ece-19 4.19.0-14-cloud-amd64 #1 SMP Debian 4.19.171-2 (2021-01-30) x86_64

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Sat Feb 27 15:04:09 2021 from 77.119.129.226
faschingbauer.joerg@fh-ece-19:~$

  • From a Windows system, use PuTTY to do the same.

Log

Day 1

Linux Basics (download), heading straight through to the “Permissions” chapter startung on slide #92.

Exercises

  • Change Password

    Your password on our cloud machine equals your username. From a security standpoint, this is suboptimal - if anybody knows your username, you’re pwned.

    Change your password.

  • Create an alias

    ls -al DIR shows a long listing of DIR (including “hidden” files). ls -al is relatively clumsy to type, clumsier than e.g. x.

    For your comfort, create an alias to solve this problem. Do this in a way that makes the alias automatically available on next login.

  • echo suppressing linefeed

    The echo command appends a linefeed (aka newline) to its output,

    $ echo this is a line because it has a newline at the end
this is a line because it has a newline at the end
$

    (You can see the newline character because the next prompt appears on a new line.)

    Which option makes echo suppress the newline character? (The next prompt appears right after the output, on the same line.)

  • Show file content

    In my (username faschingbauer.jörg) home directory, there exists a subdirectory dumpbin, and inside that directory exists a file easter.

    Print the file content on the console.

  • Create dumpbin, and give colleagues write permissions

    In your hmoe directory, create a dumpbin directory. Give your colleagues write permissions in that directory (btw, a colleague is one of the frcoll group).

  • Create a file in your colleague’s dumpbin, and write-protect that file against the colleague

Day 2

Again from Linux Basics (download)

  • Permissions, again (this is important!)

  • Tools, including some live demos of pipe usage

  • stdin, stdout, pipe short demos

../../../../_images/ssh-shell-stdin-stdout.png

How PuTTY/SSH terminals play together with the SSH daemon (the $TERM environment variable)

Day 3

  • More about SSH (download slides)

  • From Linux Basics (download)

    • IO Redirection and Pipes

    • A bunch of exercises from that same chapter

Day 4

Problem: on the (small ARM) target machine hell breaks loose (OOM killer runs amoc) from time to time. Sketch a possible way to pull memory usage snapshots from the target.

  • SSH for remote execution

  • Shell script on target

  • Python on host, after making clear why Shell is not an appropriate language if you want to do more.

../../../../_images/local-embedded-scripting.png