I'm trying to understand how terminal programs such as Fedora's package manager update a download status without printing a new line for every update. The progress indicator changes in place, for example from [ ] | 00m00s to [ ] | 01m00s, while keeping everything on one line. How does that work? I'm learning Python and want to make a smooth T-Rex runner game inside the terminal, so I need to learn how to refresh the display without flickering or leaving old frames behind.
2 Answers
For moving around the terminal more generally, programs use terminal control sequences. Tools such as tput can clear the screen, move the cursor, or erase part of a line. The terminfo database helps choose the correct sequences for the current terminal. In Python, the built-in curses module provides higher-level terminal control and is a better choice for a game with multiple moving objects, keyboard input, and screen redrawing.
The basic trick is a carriage return, written as r. It moves the cursor back to the beginning of the current line without starting a new line, so the next output overwrites the previous one. In Python, you can do something like print(f'Progress: {value}%', end='r', flush=True). Using flush=True makes the update appear immediately instead of waiting in a buffer. If the new text can be shorter than the old text, clear the line first or pad the output with spaces.
CR means carriage return: move to the start of the line. LF means line feed: move down to the next line. A normal newline usually performs both actions.