Directory Shortcuts

• . indicates the current directory.
  • It may not seem that useful, at first.
  • cd . just changes to the same directory.
  • You can use . in the paths of files, like: cat ./bird.txt
  • But cat bird.txt does the same thing, and takes two fewer keystrokes: cat bird.txt

treehouse:~/workspace$ pwd
/home/treehouse/workspace
treehouse:~/workspace$ cd .
treehouse:~/workspace$ pwd
/home/treehouse/workspace
treehouse:~/workspace$ cat ./bird.txt
There is a bird here, looking up at the statue with interest.
treehouse:~/workspace$ cat bird.txt
There is a bird here, looking up at the statue with interest.

• There are a few situations in which . is very useful, however.
  • One is in running executable programs.
  • Let me change to a directory where I have an executable stored: cd offices/web_agency/mcgavren/
  • ls
  • Here I have an executable file named hello.sh.
    • On Unix-like systems, as a safety feature, you can't run an executable file just by typing its name: hello.sh
    • You have to provide the executable's name as part of a path.
    • Using only what we've learned so far, that would mean that you have to change to the parent directory: cd ..
    • And then type the name of the directory that contains the executable, a slash, and the name of the executable file: mcgavren/hello.sh
    • You can see that it runs, and prints the message "Hi there!".
    • But that's a pain, if you're already in the same directory as the executable.
    • So you can form a path just by using . to represent the current directory, a slash, and the name of the executable: ./hello.sh

treehouse:~/workspace$ cd offices/web_agency/mcgavren/
treehouse:~/workspace/offices/web_agency/mcgavren$ ls
hello.sh
treehouse:~/workspace/offices/web_agency/mcgavren$ hello.sh
bash: hello.sh: command not found
treehouse:~/workspace/offices/web_agency/mcgavren$ ./hello.sh
Hi there!

Executable files are outside the scope of this course. But you can learn how to write a shell script, make it executable, and run it here.

• Another special symbol we've seen is .., which represents the parent directory.
  • We've already made extensive use of cd .. to change up a directory.
  • You can also use .. as an argument for commands.
  • For example, you can list the contents of the parent directory by running ls ..: ls ..
  • You can use .. as part of a path.
  • Suppose we want to change to the dentist directory that's within the parent directory.
  • We don't have to cd .. and then cd dentist.
  • Instead, we can type cd ../dentist: cd ../dentist
  • The operating system will realize this means "the parent directory's dentist subdirectory", and change directly to it: pwd

treehouse:~/workspace/offices/web_agency/mcgavren$ cd ..
treehouse:~/workspace/offices/web_agency$ ls ..
dentist  lawyer  web_agency
treehouse:~/workspace/offices/web_agency$ cd ../dentist
treehouse:~/workspace/offices/dentist$ pwd
/home/treehouse/workspace/offices/dentist

• Now for a symbol we haven't looked at thoroughly, the "tilde": ~
  • Like . and .., ~ is a reference to a directory, your user account's home directory.
  • We can type cd ~ to go to that home directory from anywhere on our system: cd ~
  • You can see that the directory path in the prompt changes to just a ~ character.
  • That's not the real path of this directory. To see the real path, we can run pwd:pwd`
  • You can see we're actually in a directory named treehouse, which is in a directory called home, which is in the root directory.
  • The name of the treehouse directory matches the name of the user account we're logged in as.
  • We can see that account name if we run the whoami command: whoami
  • Each user account has its own subdirectory under the home directory.
  • Windows and Mac machines have equivalents to the home directory, at different paths:
    • On Windows, it's at C:\Users\ (assuming C: is your primary hard drive). Also note that in the Windows Command Prompt, the ~ shortcut doesn't work.
    • On Mac OS, it's at /Users/.
  • If we run ls /home, we'll see there's only the treehouse directory.
  • That's because the treehouse account is the only one that's been created on this system.
  • If there were other users, they would be listed here, too.

treehouse:~/workspace/offices/dentist$ cd ~
treehouse:~$ pwd
/home/treehouse
treehouse:~$ whoami
treehouse
treehouse:~$ ls /home
treehouse

• So what's so special about your home directory? Why is there a special shortcut for it?
  • For ordinary users, their home directory is really the only one on your system that they should make changes to.
  • The root directory is filled with a dozen subdirectories or more.
  • Each of these directories is filled with files that the operating system relies on to run.
  • If you went around making changes in these directories, you could render your operating system unusable.
  • (Don't worry, Unix-like machines are set up so that ordinary users simply get an error message if they try to make changes in the root directory.)
  • Your home directory is the only directory on your system that's specifically intended for you to work in and make changes.
  • And that's why there's a convenient ~ shortcut to help you access it.
• Just like . and .., you can use ~ as part of a file or directory path.
  • To change to the workspace directory within your home folder, you can run cd ~/workspace: cd ~/workspace/
  • This will work no matter where you are on your system.
  • For example, I could change to the /etc directory within the root directory again: cd /etc
  • And if I run cd ~/workspace/, I'll be taken directly there.
  • Notice that I'm not typing out the whole directory name; that's because tab completion works with paths that start with ~, too.
  • These are not absolute paths, because the home directory is in different places for different users.
  • Still, using ~ does work like an absolute path, because it lets you reference files and subdirectories in your home directory from anywhere on your system.
  • Let's print out that Starbunks menu one more time, using a path relative to the home directory: cat ~/workspace/mall/starbunks/menu.txt

treehouse:~/workspace$ cd ~
treehouse:~$ cd ~/workspace/
treehouse:~/workspace$ cd /etc
treehouse:/etc$ cd ~/workspace/
treehouse:~/workspace$ cat ~/workspace/mall/starbunks/menu.txt
Venti Iced Mocha Soy Latte (with Whip): $29.99
Grande Hot Americano: $34.99
Tall Hot Chocolate: $24.99