MTEC1003 - File System

First, Some Definitions

What’s a directory? →

a directory is a cataloging structure on a file system that references other files (and directories)
we can think of it as a thing that contains files (it’s a little more complex than that, though)
they’re usually used to organize files
(technically, on OSX, a directory is a file itself! it’s a file that lists the names of items on a disk or other piece of storage media)

More Definitions

What’s a folder? →

it’s essentially the same thing as a directory
but it’s the graphical representation (like the little folder icons in finder)

Even More Definitions

What’s a pathname? →

a pathname is the general form of the name of a file or directory; it specifies a unique location in a file system
for example, in finder, to locate a file or folder, you follow a particular path - let’s check this out →.
what’s the path to the Desktop starting from the top most folder, the hard drive (probably Macintosh HD on the lab computers)? →

Some Structure

Each operating system organizes their files and directories differently. OSX’s file structure looks like this (it’s similar to other UNIX based file systems):

/ - (also called root) the top most folder on a disk (the directory that contains all of the other files and directories)
/Applications - where shared applications are kept
/Users - all user accounts and their accompanying files are stored here
/Volumes - all disks that are attached to your computer including USB drives, hard drives, etc.
/System - system specific files, libraries, preferences that are critical to the operating system

More About the User’s Directory

It’s worth noting the directories nested under Users. They should seem familiar to you.

/Users/username - (also called home when you’re in your own username’s directory) contains files specific to that particular user
/Users/username/Desktop - represents the user’s Desktop
/Users/username/Downloads - the user’s downloads folder

Path Separator

A path separator is a character that’s used to join together each directory in a pathname that contains nested directories (for example, Desktop was located under Users and username… there was a character that separated each directory).

What character represents the path separator on OSX (we just saw this)? →

it’s a forward slash, /
(sometimes just called slash when referencing directories)
it’s not backslash, \, (that’s the path separator for Windows!)

Absolute vs Relative Paths

absolute paths are paths expressed as starting from root
- example: /Users/username/Desktop
relative paths are paths expressed as relative from the current working directory
- example (if you’re starting from /Users/username): Desktop

We’ll look at this a little bit more in the next class.

Some Special Paths

There are shortcuts to represent specific paths:

~ (tilde) is your home directory
/ (slash) is root directory

The following paths are relative to the directory that you’re in:

. (dot) is the current directory
.. (dot dot) is the parent directory
../.. (dot dot slash dot dot) is the parent of the parent directory

ls

List all of the files (and directories) in the current directory. →

Think: list (we just saw this!).

$ ls
Applications	Documents   ....

ls pathname

List all of the files (and directories) in the directory specified by the pathname. →

$ ls Desktop
cuny-first.png		fractal mountains

ls -l

The -l flag gives detailed output about each file in the directory →

Think: l for long version.

$ ls -l
drwx------   3 bree  staff   102 Nov  1 15:08 Applications
drwx------+  7 bree  staff   238 Jan 28 22:46 Desktop

ls -a

The -a flag lists all files, including hidden ones →

Think: a for all.

$ ls -a
.			.config			Dropbox

ls -al

You can combine flags by placing them one after the other. This outputs a detailed list of all files. →

$ ls -al
drwxr-xr-x+ 67 bree   staff   2278 Jan 30 02:07 .
drwxr-xr-x   5 root  admin    170 Aug 13  2011 ..
-rw-r--r--@  1 bree   staff  24580 Jan 30 02:19 .DS_Store
-rw-r--r--   1 bree   staff   3459 Mar 21  2011 .RData

ls -t

The -t flag sorts by time. →

$ ls -lt
total 0
drwxr-xr-x   2 bree  staff    68 Jan 30 02:07 mtec1003
drwx------@ 19 bree  staff   646 Jan 29 21:21 Dropbox
drwxr-xr-x   9 bree  staff   306 Jan 29 19:31 projects

Combining Flags and Arguments

You can use multiple flags… and combine them with an argument as well. What do you think this does? →

$ ls -alt Desktop

It lists all of the files in Desktop (if you’re in your home folder), ordered by time, including hidden files and showing extra information.

drwxr-xr-x+ 40 bree  staff    1360 Jan 29 01:12 ..
-rw-r--r--@  1 bree  staff    6148 Jan 25 01:46 .DS_Store
drwx------+  6 bree  staff     204 Jan 24 08:26 .
-rw-r--r--@  1 bree  staff  245447 Jan 23 23:15 cuny-first.png
drwxr-xr-x  16 bree  staff     544 Oct 28 18:46 fractal mountains
-rw-r--r--   1 bree  staff       0 Aug 31 22:41 .localized

pwd

Shows the directory that you’re currently in. →

Think: print working directory.

$ pwd
/Users/bree

hostname

Prints out the name of your computer →

$ hostname
walsh-9

mkdir

Creates a directory with the name of the argument supplied. →

Think: make directory

One argument is required: the name of the directory to create.

$ mkdir my_animated_gifs

mkdir dir1/dir2/dir3

This attempts to create 3 directories nested within eachother. →

Forward slash (/) shows that a directory is within the directory preceding it. dir1/dir2 means dir2 in dir1.

However, nested directories don’t work as an argument for mkdir. (Unless…)

$ mkdir dir1/dir2
mkdir: dir1: No such file or directory

mkdir -p dir1/dir2

The -p flag allows you to create multiple directories nested within eachother. →

mkdir -p dir1/dir2
$ ls
dir1
$ ls dir1
dir2

cd

Changes current directory to the directory specified in the argument. →

Think: change directory

One argument is required: the name of the directory to change to.

$ cd Desktop
$ pwd
/Users/bree/Desktop

Using Special Paths

Let’s use special paths with cd →

$ pwd
/Users/bree
$ cd ../
$ pwd
/Users
$ ls
Shared	bree
$ cd ~
$ pwd
/Users/bree
$ cd /
$ pwd
/

Back to Directory

Pass - (dash) as an argument to cd to go back to the directory you just changed from. →

$ pwd
/Users/bree
$ cd /tmp
$ pwd
/tmp
$ cd -
/Users/bree

rmdir

Removes a directory with the name of the argument supplied. →

Think: remove directory

One argument is required: the name of the directory to remove.

$ mkdir foo
$ ls
foo
$ rmdir foo
$ ls

pushd/popd

Change to directory, but save current one for later. →

pushd requires one argument, the directory to change to.
you can pushd multiple directories
popd takes you back to the last saved directory
you can continue to use popd until there are no more saved directories

pushd/popd Continued

$ pwd
/Volumes
$ pushd ~/Desktop/
~/Desktop /Volumes
$ pushd /Applications/
/Applications ~/Desktop /Volumes
$ popd
~/Desktop /Volumes
$ pwd
/Users/bree/Desktop
$ popd
/Volumes

Activity: Drills!

Entering commands flash cards x 10 (use set 2)

We’ll do this together, then try downloading it yourself:

Download drills.py to the home directory
Type python drills.py
When prompted for a number, enter 2
CTRL-C quits

Lab

Navigating the File System

Type each command (with arguments and flags) exactly
Only press <ENTER> when instructed…
<TAB>, <ENTER>, <UP>, <DOWN> are the actual keys!
Paste answer or output below the dashed line (————)

Activity: Drills!

Entering commands flash cards x 10 (use set 12)

We’ll do this together, then try downloading it yourself:

Download drills.py to the home directory
Type python drills.py
When prompted for a number, enter 12
CTRL-C quits

Navigating the File System

Navigating the File System

Let’s Look at OSX’s Directory Structure

First, Some Definitions

More Definitions

Even More Definitions

Some Structure

More About the User’s Directory

And Now… To Pathnames!

What’s a Pathname Again?

Path Separator

Absolute vs Relative Paths

Some Special Paths

Let’s See Some Pathnames Through Finder

Now That We Know About Pathnames, We Can Navigate the File System Using the Commandline! (EXCITED YET!?)

ls

ls pathname

ls -l

ls -a

ls -al

ls -t

Combining Flags and Arguments

pwd

hostname

mkdir

mkdir dir1/dir2/dir3

mkdir -p dir1/dir2

cd

A Reminder About Special Paths

Using Special Paths

Back to Directory

rmdir

pushd/popd

pushd/popd Continued

Activity: Drills!

Lab

Activity: Drills!