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See this page as a slide show

Where are we?

“Where are we?”   “Loveland.”
“Where’s that?”   “Colorado.”
“Where’s that?”   “The USA.”
“Where’s that?”   “Earth.”
“Where’s that?”   “The Solar System.”
“Where’s that?”   “The Milky Way.”
“Where’s that?”   “You’re not from around here, are you?”

Let’s try that again.

“Where are we?”
“Loveland, Colorado, USA, Earth, Solar System, Milky Way.”

“I wanted it in the other order.”
“Milky Way, Solar System, Earth, USA, Colorado, Loveland.”

As a Unix path:
/MilkyWay/SolarSystem/Earth/USA/Colorado/Loveland

Or …

What if you’re not dealing with an idiot? Then you only need to specify as much as you need.

English: “I’m from Loveland, Colorado.”

Linux: Colorado/Loveland

Note that Colorado/Loveland did not start with a slash.

File System Basics

• The file system is a tree structure containing files
• Every file has a path that is its location, e.g., /s/parsons/d/fac/applin/monster

Paths

A pathname, or path is the “route” to a file or directory. How long is a route? It depends where you are, relative to the target.

• An absolute path is the path from the root directory, “/”. It begins with / or ~.
• A relative path is the path from the current directory
• . (dot) means the current directory
• .. (dot dot) means the parent directory

Navigating the File System

% cd
% pwd
/s/bach/a/class/cs155
% cd /s
% pwd
/s
% ls
babbage  bach  beethoven  chopin  chromatin  fir  jawar  lovelace  parsons  red

• Navigating the file system is the first Unix skill you will learn
• Our first Unix commands:
  • pwd: print working directory
  • ls: list directory
  • cd: change directory
  • more: view a file

The Structure of a Unix Command

• command [option] ... [file] ...
• verb [modifier] ... [noun] ...
• action [modifier] ... [object] ...

Options can modify behavior.

ls

% cd ~/pub/hw1Files
% ls
hw1_file  hw1_prog  hw1_prog.c
% ls -l
total 20
-rw-r--r-- 1 cs155 class   96 Dec  9  2017 hw1_file
-r-xr-xr-x 1 cs155 class 8224 Jan 10  2018 hw1_prog
-rw-r--r-- 1 cs155 class  881 Jan 10  2018 hw1_prog.c
% ls -lF
total 20
-rw-r--r-- 1 cs155 class   96 Dec  9  2017 hw1_file
-r-xr-xr-x 1 cs155 class 8224 Jan 10  2018 hw1_prog*
-rw-r--r-- 1 cs155 class  881 Jan 10  2018 hw1_prog.c

• Take ls as an example
  • -l : use a long listing format
    that’s a lower-case L
  • -S : sort by file size
  • -F : Put / after directories, and * after programs.

Also, there’s ll (that’s ell-ell, not eleven), which is same as ls -l. It’s a non-portable alias, which we will discuss later.

Home Directories

% echo Hi there, folks!
Hi there, folks!

% echo ~
/s/bach/a/class/cs155

% echo ~davematt
/s/parsons/c/fac/davematt

% echo ~bin
/bin

% echo ~/bin
/s/bach/a/class/cs155/bin

% echo ~cs155/bin
/s/bach/a/class/cs155/bin

• Your home directory is where you are when you login to a unix system
• ~ means your home directory
• ~name means somebody else’s home directory
• ~bob is bob’s home directory
• ~/bob is the directory bob inside your home directory
• The command is cd ~ or cd ~bob, not just ~.
  ~ is an noun, not a verb.

No memorization of paths

• If you ever catch yourself typing /s/bach/…, then you’re doing it wrong.
• You should be using ~ instead.
• I don’t know the full path of my home directory, because I use ~.

ls subtlety

% cd ~/pub

% ls -l hw1Files
total 20
-rw-r--r-- 1 cs155 class   96 Dec  9  2017 hw1_file
-r-xr-xr-x 1 cs155 class 8224 Jan 10  2018 hw1_prog
-rw-r--r-- 1 cs155 class  881 Jan 10  2018 hw1_prog.c

% ls -ld hw1Files
drwxr-xr-x 2 cs155 class 4096 Jan 10  2018 hw1Files

• Consider ls -l hw1Files, where hw1Files is a directory (folder).
• We recall that -l means a long listing.
• However, do we get a long listing of the files within that directory, or a long listing of the directory itself?
• You get a long listing of the contents of the directory.
• Use -d to say “I want a listing of the directory itself.”

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