Text files

Part 3: Text File Manipulation

You can use the CLI to do simple or complex text manipulation. As developers, you will use a text editor or IDE like IDLE, PyCharm, or VSCode to do such tasks most of the time. However, it can be handy to do from the CLI sometimes, and many scripts used to compile and build software these CLI text-manipulation techniques.

Key terms

Most CLI commands, including the ones you have already seen like ls and pwd have an output that is printed to the terminal. Some commands, like cp, do NOT have an output printed to the screen.

Below you will see the special > and >> operators.

• > is the redirect operator. It takes the output from a command and writes it to a file you specify, e.g., echo "hello" > file.txt. It will create the file if it does not exist, and will overwrite the file if it does exist!
• >> is the append operator. It will create the file if it does not exist, and will append to the end of the file if it does exist!

Viewing and Editing Text Files

• echo - Display a line of text
• cat - Concatenate and display file contents
• less - View file contents one screen at a time
• grep - Search for patterns in Files

echo "Hello, Linux CLI!" > hello.txt
cat hello.txt
echo "Another line" >> hello.txt
cat hello.txt
grep "Hello" hello.txt
grep "o" hello.txt

seq 1 1 10000 >> numbers.txt  # making a big file - no need to learn. 
cat numbers.txt
less numbers.txt # Spacebar goes forward, b goes back, q to quit.

Exercise

1. Use echo to create a text file with some content. Try echo "this is my first file" > myfile.txt
2. Use cat will print all of the file’s contents to the screen all at once.
3. Use echo to append text to the file.
4. Use grep to search for the word “first” in the file.
5. Use less to view the file content one screen at a time. Hit q to exit.

Knowledge check

• Question: How can you append text to an existing file using echo?
• Question: What command would you use to search for a specific word in a file?