How do I use the command-line shell?

In CSE 140, you use two tools to run Python programs: IDLE and the command-line shell. This is a small guide in using the shell.

The command-line shell, sometimes called the command prompt or the terminal, is a tool that lets you control your computer using only textual commands. It offers a lot of power and simplicity (simplicity is different from ease of use).

Just like with a graphical file browser such as the Finder or Windows Explorer, there is a "current directory" that you are currently working in. ("Directory" and "folder" are synonyms.) You can issue commands that operate in that directory, or you can change the current directory.

This guide presents an example transcript of using the shell for Unix (Mac/Linux) and Windows machines. The transcript assumes that the student has already installed the Enthought Python Distribution as described in the Computing Resources page, and has used other programs such as the Finder or Windows Explorer to download his/her homework into a directory. When you run similar commands, there may be slight differences from the example transcript, such as the number, names, and times of files.

See the section that is relevant to you:

• Mac/Linux
• Windows

Mac/Linux

Here are most of the commands you will need to use:

• pwd - print the absolute pathname of your current working directory
• cd directory - change your working directory to the given directory
• cd .. - change your working directory to the parent of the current working directory
• ls - list the contents of the current directory ("ls" is short for "list")
• python - run the Python interpreter
• python program.py - run the Python program that is stored in the program.py file

You can open a command-line shell by running the terminal program.

In the below example transcript, $ is the prompt at which the user types commands. Boldface text was typed by the user, and non-boldface text was printed by the command-line shell.

  
  $ pwd
  /home/me
  $ ls
  Desktop    Downloads  Music  Pictures     Public    Templates   Videos
  Documents  Dropbox    Old    Programming  Software  Ubuntu One  VirtualBox VMs
  $ cd Desktop 
  $ pwd
  /home/me/Desktop
  $ ls
  CSE140
  $ cd CSE140 
  $ pwd
  /home/me/Desktop/CSE140
  $ ls
  homework1  homework2
  $ cd homework2 
  $ pwd
  /home/me/Desktop/CSE140/homework2
  $ ls
  answers.txt  data  dna_analysis.py  expected_output
  $ python dna_analysis.py data/test-small.fastq 
  GC-content: 0.3
  

Windows

Here are most of the commands you will need to use:

• echo %cd% - print the absolute pathname of your current working directory
• cd directory - change your working directory to the given directory
• cd .. - change your working directory to the parent of the current working directory
• dir - list the contents of the current directory ("dir" is short for "directory")
• python - run the Python interpreter
• python program.py - run the Python program that is stored in the program.py file

You can open a command-line shell by running the cmd program.
You should have a Command Prompt shortcut located in the Start Menu, in the Accessories submenu of All Programs, or on the Apps screen for Windows 8. About.com has more detailed instructions about starting the command prompt.

In the below example transcript, text such as C:\Users\Me> is the prompt at which the user types commands. Boldface text was typed by the user, and non-boldface text was printed by the command-line shell. Also note that in this example transcript, much irrelevant output has been suppressed in order to emphasize the important information.

  C:\Users\Me>echo %cd%
  C:\Users\Me

  C:\Users\Me>dir
   Directory of C:\Users\Me

  06/02/2012  08:11 PM    <DIR>          .
  06/02/2012  08:11 PM    <DIR>          ..
  07/18/2012  05:03 PM    <DIR>          Contacts
  01/10/2013  07:24 PM    <DIR>          Desktop
  07/18/2012  05:03 PM    <DIR>          Documents
  01/09/2013  09:59 PM    <DIR>          Downloads
  07/18/2012  05:03 PM    <DIR>          Favorites
  07/18/2012  05:03 PM    <DIR>          Links
  07/18/2012  05:03 PM    <DIR>          Music
  11/28/2012  09:19 PM    <DIR>          Pictures
  11/29/2012  01:42 AM    <DIR>          Saved Games
  07/18/2012  05:03 PM    <DIR>          Searches
  11/27/2012  09:06 PM    <DIR>          Videos

  C:\Users\Me>cd Desktop

  C:\Users\Me\Desktop>dir
   Directory of C:\Users\Me\Desktop

  01/10/2013  07:25 PM    <DIR>          .
  01/10/2013  07:25 PM    <DIR>          ..
  01/10/2013  07:25 PM    <DIR>          CSE140

  C:\Users\Me\Desktop>cd CSE140

  C:\Users\Me\Desktop\CSE140>dir
   Directory of C:\Users\Me\Desktop\CSE140

  01/10/2013  07:25 PM    <DIR>          .
  01/10/2013  07:25 PM    <DIR>          ..
  01/10/2013  07:25 PM    <DIR>          homework1
  01/10/2013  07:24 PM    <DIR>          homework2

  C:\Users\Me\Desktop\CSE140>cd homework2

  C:\Users\Me\Desktop\CSE140\homework2>dir
   Directory of C:\Users\Me\Desktop\CSE140\homework2

  01/10/2013  07:24 PM    <DIR>          .
  01/10/2013  07:24 PM    <DIR>          ..
  01/06/2013  05:28 PM               519 answers.txt
  01/10/2013  07:24 PM    <DIR>          data
  01/09/2013  09:26 PM             1,866 dna_analysis.py
  01/10/2013  07:24 PM    <DIR>          expected_output

  C:\Users\Me\Desktop\CSE140\homework2>python dna_analysis.py data\test-small.fastq
  GC-content: 0.3