Getting to know your way around
Getting to know your way around
Locate and open your terminal
The first stuff you see in your terminal is called the prompt.
It will include your username, where you are, and what machine this terminal is on.
By default:
machine_name:current_directory username$
username@machine_name:current_path$
username@machine_name current_path
$
In general, most systems will open a terminal in your home directory
This is a folder on the computer filesystem that belongs to you.
You put your work here, configure settings for many programs and so on.
You can see where you are using the shell command pwd
Type that command into your terminal now
The pwd command shows the present working directory
OSX
$ pwd
/Users/cewing
Linux
$ pwd
/home/cewing
Windows (git-bash)
$ pwd
/c/Users/Cris Ewing
In any computer system, a path represents a location in the filesystem.
Paths are like addresses, listing a location from the general to the specific.
A bit like addressing an envelope backwards:
vs.
A path is absolute when it starts with /
A path is relative when it does not
Is the path returned by the pwd command absolute or relative?
Movement is basic to life.
All operating systems distribute resources among many directories
To be a power user of the command line, you must be able to move around.
The command for moving from one directory to another is called cd
You can supply a path to tell the terminal the address where you want to go
This path can be absolute or relative.
The cd command allows you to change directories
It can take a path as an argument (absolute or relative)
What happens if you do not supply a path to indicate where you want to go?
Before we begin, use pwd again to show the path to your home directory
Write this value down
You'll use it in a moment to get back
Now type the following command at your prompt:
OSX/Linux:
$ cd /
Windows:
$ cd /c
You've just changed directories.
The address you supplied to the cd command was for the root of your computer
(Windows users, this isn't exactly true, but it's true enough for today)
This is the very topmost container in your filesystem
Everything else is located inside this directory, or in a directory whose path starts here.
paths that start with the root are absolute because there can be no ambiguity about where to start looking
The root is the topmost container of a computer filesystem
Everything on the computer can be said to be contained in the root or in a container that is contained there
Absolute paths always begin with the root, so that there is no doubt about where to begin moving through the filesystem
The root is generally restricted to administrative users
You should never delete anything located directly in the root
Now that you're here at the root of your computer filesystem, you might want to see what's here.
To list the contents of your present working directory, you'll use the ls command.
Type this command at your prompt:
$ ls
You should see something like this:
OSX:
Applications Users dev net tmp
Library Volumes etc opt usr
Linux:
bin etc lib lost+found opt run srv usr
boot home lib64 media proc sbin sys var
Windows:
$Recycle.Bin Documents and Settings Recovery autoexec.bat
BOOTSECT.BAK PerfLogs System Volume Information bootmgr
Like many unix-style shell command, the behavior of ls can be modified
By default, it shows the names of items in your present working directory in alphabetical order
By providing the command with flags, we can modify that
For example, the t flag changes the order of the listing so that the most recently modified items are first.
You can supply a flag to a command with the - sign, like so:
$ ls -t
Try it out now.
Clearly, the ordering changes, but is it really sorting by modification time?
The l flag changes the listing shown to long format
This will display permission, ownership and modification information about each item in the directory:
$ ls -l
drwxr-xr-x 2 root root 4096 Sep 23 12:08 bin
drwxr-xr-x 3 root root 4096 Nov 5 15:25 boot
...
You can combine flags by adding each to a single -
Try this:
$ ls -lt
We have a command that lists items alphabetically
We can modify it to list them by modification date, with the most recent first.
What if we want to reverse the ordering?
The r flag (note that that is a lower-case r) does this.
Try using that flag by itself
Try combining it with the t flag
Try combining it with l and t
The ls command shows you a listing of the contents of your present working directory
The behavior of this command can be altered by flags
The l flag returns the listing in long format
The t flag returns the listing ordered by modification time
The r flag reverses the order of the listing
Unix commands may be modified by providing flags
Each flag changes the behavior of a command in a single, simple way
The flags can be combined to produce more complex changes
Flags are provided by using the - sign after the command
How can you know what flags may be used for a given command?
Unix-like systems provide a system command called man (short for manual)
You provide this command the name of another command
It will return a manual explaining how that command works and what options it provides
Type the following command at your prompt:
$ man ls
Windows users, this will not work for you
Instead, use your web browser and type the same command into your search bar
Teh Google will provide
The man command provides access to the built-in manual for all unix commands
Providing the command with the name of some other command will print detailed information about how that command may be used
Often these manual pages include useful examples for common and advanced usage patterns
Spend the next five to ten minutes trying out different flags to the ls command
For each flag you try, make a prediction about the effect it will have
After trying it, review your prediction
Were you right?
If not, in what way were you wrong?
What happened that surprised you?
These sorts of surprises are the seeds of learning, treasure them
Okay. Enough poking about here at the root
Let's head back to our home directory
You wrote down the path returned by the pwd command as we were leaving.
Can you get back there now?
$ cd /Users/cewing
Some of you may have a bit of difficulty at this point
For example, Windows users may have a path for their home directory that looks like this:
/c/Users/Cris Ewing
$ cd /c/Users/Cris Ewing
sh.exe": cd: /c/Users/Cris: No such file or directory
The problem is the space between my first and last names
The command line expects paths to be a single continuous string of characters
Spaces are used to delimit one element of the command line from the next
So how do we cope with this?
The secret lies in tricking the command line into thinking that the space is just another character like any other letter or number
You can do this by escaping it with the \ character
Try typing this instead:
$ cd /c/Users/Cris\ Ewing
How'd that work?
This brings up the idea of unix naming conventions
In general, unix power users tend not to use spaces in the names they give to things.
Use dashes (-) or underscores (_) to separate words in names
This will help as you start working with software systems that don't play nicely with spaces in path names.
It gets easier to do this as you use the command line more
One other interesting issue to cover here is the question of case sensitivity
Linux is a case sensitive operating system
This means that the names foo.jpg and FOO.JPG are not the same
OSX and Windows are case insensitive, which means those two names are the same
(however, in terminals, unix command names are case sensitive)
Most unix power users tend to write all names in lower-case letters.
(bonus: you don't have to use the shift key when you do)
Avoid spaces in the names you give to files and directories
Use dashes and underscores to create visual separation between words in names
Prefer lower-case letters in naming files and directories
So far, we've used cd to move to the root of our filesystem and back
Each time we've provided an absolute path as an address to where we'll go
But we can also use relative paths as addresses
When we do, they are considered to be relative to where we are now
In other words, relative paths are always construed by the OS as beginning with the value of pwd
Use the ls command to see what you have here in your home directory
Use the l flag to get the long format
Notice that some of the entries in the list start with a d and some begin with -
Those that begin with d are directories, pick one
Use the cd command, providing the name of your chosen directory as a relative path
Now, make a prediction about the path of your present working directory
Finally, use the pwd command to confirm or reject your prediction
Repeat the exercise, moving further down from your home
You've now moved several levels down from your home directory, but how to get home?
You could provide the absolute path of your home directory, you've done that before
But let's mix it up a bit
In unix systems, the symbol .. (two periods) stands for "one filesystem level above where I currently am"
You can use this relative path with the cd command to move up one level
Try it:
$ cd ..
You can even chain them together, providing relative paths that go up more than one level:
$ cd ../..
And you can combine these with directory names to go back down into a different branch of your filesystem:
$ cd ../somewhere-else
Take the next five to ten minutes to explore your filesystem
Use the ls command to find directories in your present working directory
Use the cd command to move down into and back up out of various directories
Use relative paths and the .. symbol
Finish when you are somewhere not in your home directory
Do you know the exact command to give to get home from wherever you are?
Remember back a while, when you tried the cd command without a path?
Try it again:
$ cd
Where are you now?
Is that what you thought it did before?
You've seen how .. is interpreted by the command line to mean "one level up from here"
That's not the only symbol you have to work with
Use cd, ls and .. to move away from your home directory again
When you've moved away three or four steps, try this:
$ ls ~
That squiggle after the ls command is a tilde
You can find it in the upper left corner of your keyboard
Your command line replaces that symbol with the absolute path of your home directory
One other item of note in that last command
You provided a path to the ls command, what was the result?
In fact, the ls command can list places other than where you are now, if you provide a path
Try listing the root: ls /
Try listing a directory located at the root
Try combining a path with flags to the ls command
Does the order in which you give the two make a difference?
In point of fact, if you don't give ls a path, it simply assumes you mean "right here"
You can make this explicit by using the . symbol (one period)
Just as .. means "one level up from here", . means "right here"
Does ... mean "two levels up from here"?
You can use the .. symbol as an element in a path (absolute or relative) as a shortcut for "one level up"
You can use the . symbol as an element in a path as a shortcut for "right here"
You can use the ~ (tilde) as a shortcut for the absolute path of your home directory
You can use the cd command without an argument to return to your home directory immediately from anywhere
Take a moment to reflect
You've learned and used the following commands:
| command | purpose |
|---|---|
| pwd | obtain the absolute path of the present working directory |
| cd | change directories to the path provided (or home if none) |
| ls | list the contents of the provided path (or here if none) |
| man | get information about the options and usage for any command |
You've also learned the following concepts:
Don't close your terminals yet!
You've earned it