CMPSC 311 - Introduction to Systems Programming UNIX Essentials

CMPSC 311 - Introduction to Systems Programming UNIX Essentials

The Unix Philosophy

• Write programs that do one thing and do it well.
• Write programs to work together.
• Write programs to handle text streams, because that is a universal interface. -- Doug McIlroy, Unix patriarch
• More general programming principles:
  • KISS – “Keep it simple, stupid”
  • Modularity – thinking in terms of components
  • Composability – thinking in terms of interacting components
  • Transparency – making inspection and debugging easier

Command Line Interface

• Command line: Efficient, powerful, scriptable, simple, and reliable.
• Always works, even if everything else is broken.
• What is it?
  • Shell program (“bash” on Linux)
  • Interprets built-in commands
  • Runs other programs
  • Runs shell scripts

Standard Filesystem Layout

• Grouped by type
  • / root directory of the entire filesystem
  • /usr installed software
  • /usr/bin, /usr/lib, …
  • /etc configuration
  • /home users’ own files
  • /dev devices
  • /tmp temporary files

Root (administrator)

• Files in Unix have owners
• Users can (usually) only touch their files
• Root (Super User) can do anything
• "Becoming root"
  • Administrative privileges: su
  • Temporary privileges (per command): sudo (su “do”)
• Important principles for administrators:
  • Respect the privacy of others.
  • Think before you type.
  • With great power comes great responsibility.

Navigating the CLI

• Files
  • Listing: ls
  • Moving/copying: mv
  • Deleting: rm
  • Reading: cat
  • Creating: touch
• Directories
  • Print working dir (“You are here”): pwd
  • Change dir ("moving around"): cd
  • Creating/removing: mkdir, rmdir
• Special directory names
  • . means the current directory
  • .. means the parent directory
  • ~ means home

Help!

• Built-in option to most commands: help
• Everything else: man
  • Standard layout
  • man operator
  • man ascii
  • man man!
• Get used to reading these!
• Keyword search: man -k
• (Also Google)

Editing Files

• Unix philosophy again: text is important!
  • Configuration? Text files.
  • Scripting? Text files.
  • Programming? Text files.
• Vim (and vi)
  • Do one thing and do it well
• Graphical Editors (i.e. Notepad, gedit)
• More advanced editors
  • Sublime Text
  • Visual Studio Code

Why Learn A CLI Editor?

• It’s fun!
• Debugging systems remotely
• Complex things break
• Embrace the command line
• Vim: Run vimtutor at the command line
• GVim for Windows, MacVim for Mac
• Many, many, many features/extensions
• GNU Nano: Run nano at the command line

Shell Scripting

• Getting tired of typing the compile command yet?

• Shell script = list of commands to run

• Put this in a file called build.sh:

  #!/bin/sh
  make clean
  make
  ./cmpsc311-f21-assign1 < test-input1.txt
  

• Now just run (or ./build.sh if you gave execution permission first: sudo chmod +x build.sh)

• Example execution:

  $ sh build.sh