Software Tools

(COMS10012 / COMSM0085)

Lecturers:

• Joseph Hallett
• Matthew Edwards
• Manolis Samanis

Unit Director:

• COMS10012: Joseph
• COMSM0085: Matthew

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Unit Structure

• 2 workbooks every week, with guidance & video introductions
  • All on unit website https://cs-uob.github.io/{unit}
• 1 intro lecture (Tuesday @ 11:00 in Phys 1.11)
• 1 3-hour lab session (Friday in MVB 2.11)

Part 1:

1. System administration (ssh,vagrant,apt)
2. Version control (git)
3. Shell scripting (sudo,grep,sh) and build tools (make,javac,pip)
4. Debugging (gdb,strace,ltrace)
5. Databases (mariadb, SQL)

Part 2:

1. The Web (HTTP, HTML)
2. Stylesheets (CSS)
3. Dynamic content (Javascript)
4. Web scraping (wget, BeautifulSoup)
5. Practical encryption (gpg, OpenSSL, LetsEncrypt)

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Assessment for COMS10012

One 2-hour paper-based multiple-choice exam.

• Taken during the summer assessment period (13th - 31st May).
• Questions will be drawn from across Part 1 & Part 2 of the unit.
• Notes are permitted.

Plus: completion of the mandatory attendance hurdle for labs.

Resit

• Different exam of the same format.
• Taken during the reassessment period (5th - 15th August).

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Assessment for COMSM0085

Combined result of 2 in-class tests. Each will be:

• 1 hour long.
• Blackboard examination taken under exam conditions in MVB 2.11.
• Combination of multiple-choice, true/false and fill-in-the-blanks
• Notes (and use of the shell) are permitted.
• No language-assistance tools, AI help or similar are permitted.

Part 1

• Test takes place after Reading Week (Week 6 of TB2)
• 16 questions across all of Part 1

Part 2

• Test takes place in Week 11 (after end of Part 2)
• 16 questions across all of Part 2

If you pass on the combined result of Part 1 & Part 2, you pass (even if you failed one test).

If you fail on the combined result, you fail (even if you passed one test).

Short mock exams will be made available.

Resit

• 2-hour paper-based multiple-choice exam.
• Taken in person during the resit period.
• Questions covering both Part 1 & Part 2.
• Notes are permitted (but nothing else).

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Expectations

• Approach workbooks with the intent to learn.
  • Blindly copying-and-pasting from the workbook often won’t work.
  • You will be assessed in part on your ability to apply tools to new problems.
• You are expected to start the workbooks before the Friday lab.
  • Watching intro videos for the first time in the lab is a poor use of contact time!
  • There is (intentionally) too much content to easily finish within the lab session.
  • Make the best use of the TAs and lecturers – get stuck before you go to the lab, and there’ll be more time to help you.
• Don’t be afraid to ask.
  • Use the Teams channel to raise problems or queries. Other people benefit!
  • Sometimes we make mistakes – if you point it out we can act on it.
• Attend the labs.

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Week 1: POSIX Systems

We will be covering:

Workbook 1: System Administration

(or, “A Sysadmin’s Illustrated Primer”)

• Using ssh to access the lab machines remotely.
• Setting up key-based SSH login (in the workbook).
• Vagrant, your Debian setup, and why we’re using it.
• Installing packages on Debian.

Workbook 2: The POSIX shell

(or, “grep gud”)

• Shell basics: globbing, arguments, and variables.
• Pipes, and why ‘plumbing’ is essential to using the shell effectively.
• Regular expressions (with grep and sed)

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Workbook 1 Preview: SSH

Goal: log in to the lab machines remotely (so we can do exercises from our beds)

Secure Shell – tool for secure remote shell sessions.

Requires the machine we want to log in to (the host) to already be running sshd – the ‘daemon’ that handles SSH connections.

ssh user@host

Problem: The lab machines aren’t directly accessible over the internet.

ssh user@seis.bris.ac.uk

SEIS: Not a lab machine, but accessible from the internet.

ssh user@rd-mvb-linuxlab.bristol.ac.uk

A load-balancer randomly assigns us to a lab machine!

user@host:~$

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Workbook 1 Preview: Vagrant

Some of the things you will do in this unit require admin rights.

But we don’t want to give you admin rights to the lab machines.

Solution: Virtual machines managed by a container system (vagrant).

You can freely reconfigure, install software, destroy the OS, etc.

Write a Vagrantfile which specifies the configuration.

vagrant up to launch the VM.

vagrant ssh to log in to the VM.

vagrant halt to shut down the VM.

On the lab machines: VM storage isn’t persistent.

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Workbook 2 Preview: Grep

Global Regular Expression Print.

Regular expressions are a series of characters that define a pattern that we want to select or find within a piece of text. The regular expression rules form a primitive grammar (a Type 3 on the Chomsky hierarchy) that can be used for specific purposes.

grep pattern file

The patterns can be sequences you want to find.

grep ench /usr/share/dict/cracklib-small

But also include control characters with special meaning

grep ^ench /usr/share/dict/cracklib-small

grep ench$ /usr/share/dict/cracklib-small

grep ^..ench..$ /usr/share/dict/cracklib-small

Searching for patterns in text is an extraordinarily common task for programmers, and regular expressions are much more powerful than the above indicates.

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Workbook 2 Preview: Pipes

Some other tools: head, tail, less wc -l.

But how can we combine these tools?

Pipes connect Unix tools together.

grep ench /usr/share/dict/cracklib-small | head

grep ench /usr/share/dict/cracklib-small | head -10

grep ench /usr/share/dict/cracklib-small | head -10 | wc -l

grep ench /usr/share/dict/cracklib-small | head -10 | tail -1

grep ench$ /usr/share/dict/cracklib-small | sed 's/ench/itch/' | less

With pipes, Unix tools (that ‘do one thing well’) can be stitched together into powerful single-use systems to accomplish difficult tasks.

Implements a form of software modularity & reusabilty, accessible at your primary interface with the OS.

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The End

We’ll see you on Friday.