The command line is a text-based interface to your computer (or a computer in the cloud). It allows you to perform actions on the computer by running commands.
In (Google Colab / Jupyter) notebooks, you can execute these commands by prefixing them with the ! character.
Therefore, you could, for example, run !ls in a notebook cell to list all files in the current folder.
Please note: The command line is a very powerful and useful tool worth exploring. However, this very short primer is only going to introduce you to some very basic commands that will help you during this workshop.
When you are using the command line, you are always 'within' a folder on your file system. The folder you are in can be identified by a path, for example /home/linguistics/exercises. In this example, there is a folder called exercises which is in a folder called linguistics which is in a folder called home which is in the so-called root directory / of the file system.
Similarly, if you git clone this repository, you will have, for example, this folder: python-programming-for-linguists/2020/data/wikipedia.
If you want to know your current folder, you can run the pwd command on the command line.
If you want to move to a different folder, you can run cd path (e.g., cd python-programming-for-linguists/2020/data/) to change the directory. You can also use cd .. to go up one folder. Therefore, if you are in python-programming-for-linguists/2020/data/ and rund cd .., you will end up in python-programming-for-linguists/2020/.
If you want to know which files are in the current folder, you can run ls.
You can create an empty file in the current folder using touch filename (e.g., touch exercise.txt).
If you want to have a brief look at the contents of a file, run cat filename (e.g., cat exercise.txt).
In order to copy a file, you will need to run cp filename copy_of_filename. For example, you could run cp exercise.txt exercises/exercise.txt to copy the file exercise.txt into a folder called exercises. In case you want to move the file, you can use mv instead of cp.
If you need to delete a file, you can run rm filename (e.g., cat exercise.txt).
Find a specific string in a file
cat file.txt | grep 'search term'
Replace every instance of word_a with word_b in file file.txt
sed 's/word_a/word_b/g' file.txt
Display the differences between file_a.txt and file_b.txt
diff file_a.txt file_b.txt
Count the lines, words, and characters in file.txt
wc file.txt or wc -w file.txt to just get the word count.
I have also prepared a video tutorial on using the Linux shell. This Shell Primer for Linguistics is available via YouTube.