intro_to_command_line.md

The Command Line

Materials

MacOS

• Laptop
• Terminal

Windows 10

• Laptop
• Anaconda Powershell

Installation

MacOS

1. Click here to download the latest version of Anaconda Navigator for MacOS
2. Once the download has finished run the installer

Windows 10

1. Click here to download the latest version of Anaconda Navigator for Windows 10
2. Once the download has finished run the installer

Getting to the Command Line

MacOS

1. Navigate to Finder > Applications > Utilities > Terminal
2. Run the Terminal, you should see something that looks like this:

Windows 10

1. Navigate to Anaconda Powershell (it should be in the Start menu)
2. Run the Anaconda Powershell

Note: who would like to take a screenshot of the Anaconda Powershell and send it to me? Thx!

Command Prompt

MacOs

$

Windows 10

>

The command prompt, illustrated above per operating system, indicates to a user where they can enter commands (type things)

Moving Around

• pwd: or print working directory, shows the directory you are currently in
• ls: lists all contents of a directory (folder)
• cd: or change directories, use this to move to a different part of your computer

Demo

1. check the current working directory (where you are on your computer): pwd

   note you should be in the home directory

2. list the contents of the home directory: ls

3. choose a FOLDER to open, or change the working directory, with cd: cd FOLDER

   for example cd Downloads

   note the command line has autocomplete, hit TAB as you type characters to try to use it!

4. hit ENTER to run the command

5. check the command prompt, notice anything different?

   my command prompt (for example)

   • before step 4 (base) 95-mdpmclapca:~ cta$
   • after step 4 (base) 95-mdpmclapca:Downloads cta$

6. confirm that the present working directory has changed: pwd

7. list the contents of the FOLDER directory (Downloads in my example): ls

8. return to the home directory with this SUPER FUN SHORTCUT: cd ~

9. confirm that the present working directory is now the home directory: pwd

10. note that the command prompt has returned to its default state

    my command prompt (for example) (base) 95-mdpmclapca:~ cta$

File Input / Output

• mkdir: make and name a new directory
• touch: make and name a new file
• echo: outputs the strings being passed as arguments
• >: overwrite data in a file (if the file exists)
• >> : append data to a file (if the file exists)
• cat: reads data from a file and outputs the data
• nano: or GNU nano, a text editor

Demo

1. make a new FOLDER with mkdir: mkdir DATA

2. change directories into DATA: cd DATA

3. confirm that the present working directory has changed: pwd

4. make a new .txt file with touch: touch data.txt

5. confirm that data.txt is present in DATA: ls

6. we can print messages at the command line with echo: echo "Hello World"

7. we can also use echo to pass information into a file with >: echo 'data1' > data.txt

8. confirm the contents of our file with cat: cat data.txt

9. let's say we have 2 data points, try adding data2 to our file with the following: echo 'data2' > data.txt

10. confirm the contents of our file with cat, see any issues here?: cat data.txt

11. cat reveals that the command in step 9 has overwritten data1 with data2

12. let's repeat our procedure and overwrite data2 with data1: echo 'data1' > data.txt

13. here we use >> to append data2 to data.txt: echo 'data2' >> data.txt

14. confirm the contents of our file with cat: cat data.txt

    you should see both data1 and data2

15. another way to explore files via the command line is with nano, the command to launch teh GNU nano text editor. Open data.txt in nano: nano data.txt

16. you can navigate through data.txt with the arrow keys and will notice a rather old-fashioned User Interface at the bottom of the window. Ctl-X to exit