Unrar Behavior During Terminal Resizing

This article explains how the unrar command-line utility behaves when a terminal window is resized during an archive extraction. While the core file decompression and writing processes continue uninterrupted, the program's console output often suffers from visual formatting glitches because unrar does not actively redraw or reformat its standard output stream to accommodate dynamic window dimensions.

Signal Handling and Core Execution

When a terminal window is resized, the operating system kernel sends a SIGWINCH (Window Change) signal to the active foreground process. Advanced terminal applications built with libraries like ncurses catch this signal to calculate new window bounds and repaint the user interface.

The standard unrar utility does not implement an active dynamic redraw mechanism for SIGWINCH. Because terminal window changes do not terminate the process, the background extraction logic remains completely unaffected:

  • Decompression Integrity: Data decompression runs without pauses or errors.
  • File System Operations: Files continue to write to disk normally.
  • Exit Codes: The operation will exit with standard success or failure codes regardless of window adjustments.

Visual Output and Artifacting

The primary impact of resizing a terminal during an unrar extraction is visual. By default, unrar prints extraction progress, file names, and percentages using carriage returns (\r) to overwrite the current line in standard output rather than scrolling continuously.

When the terminal size changes mid-operation:

  • Shrinking the Terminal Width: If the terminal width becomes narrower than the line of text being printed, the terminal emulator forces the text to wrap onto a new line. When unrar issues a subsequent carriage return to update the progress percentage, it only returns to the start of the current wrapped line rather than the original line. This causes repeated, cascading lines of progress output and cluttered text on the screen.
  • Expanding the Terminal Width: If the terminal is widened, previously wrapped lines do not automatically unwrap. Furthermore, because unrar does not issue terminal clear sequences, shorter output lines may leave "ghost" characters from longer, previously printed lines visible on the right side of the screen.

Suppressing Display Issues

To prevent display artifacts during automated tasks or environments where window resizing is frequent, you can control unrar's verbosity using built-in switches:

  • Disable percentage indicators: Using the -idp switch disables the dynamic percentage indicator while still displaying extracted filenames, reducing line-overwrite issues.
  • Quiet mode: Using the -idq switch restricts output to basic messages.
  • Complete silence: Using the -inul switch suppresses all console messages, directing errors strictly through process return codes.