A minimal C library that implements a command line with history for VT100 compatible terminals.

The user interface is a minimal subset of readline's default key bindings:

• Movement
  • Ctrl-a: Move to the start of the line.
  • Ctrl-e: Move to the end of the line.
  • Ctrl-f: Move forward a character.
  • Ctrl-b: Move back a character.
• Editing
  • Backspace: Delete the character before the cursor.
  • Ctrl-d: Delete the character under the cursor.
  • Ctrl-t: Transpose the character under the cursor with the previous one.
• Cutting
  • Ctrl-k: Kill forwards to the end of the line.
  • Ctrl-u: Kill backwards to the start of the line.
  • Ctrl-w: Kill backwards to the start of the current word.
• History
  • Ctrl-p: Fetch the previous command in the history.
  • Ctrl-n: Fetch the next command in the history.
• Session
  • Tab: Auto-complete current input.
  • Ctrl-l: Clear the screen.

The implementation is a BSD-licensed C99 library with about a thousand lines of code in a single file, alongside a header that declares the public API.

Building Comlin requires a reasonably modern POSIX system with a C99 or newer compiler. It works on terminals that support a minimal, widely-supported set of characters and VT100 escape sequences.

Output sequences are written to the terminal (typically stdout) to update the display. One character, ASCII CR (Carriage Return 0D), is used specially to move the cursor the start of the current line. The other output sequences stem from the VT100:

• EL (Erase Line): ESC [ n K
  • If n is 0 or missing, clear from cursor to end of line.
  • If n is 1, clear from beginning of line to cursor.
  • If n is 2, clear entire line.
• CUF (CUrsor Forward): ESC [ n C
  • Move the cursor forward n characters.
• CUB (CUrsor Backward): ESC [ n D
  • Move the cursor backward n characters.

Basic functionality requires only these, but others may be used conditionally. If getting the terminal width via the TIOCGWINSZ ioctl fails, it will be requested from the terminal (as if via a serial line):

• DSR (Device Status Report): ESC [ 6 n
  • Report the current cursor row n and column m as ESC [ n ; m R.

If that method fails as well, the terminal is assumed to be 80 columns wide. If multi-line mode is enabled, the cursor may be moved vertically:

• CUU (Cursor Up): ESC [ n A
  • Move the cursor up n lines.
• CUD (Cursor Down): Sequence: ESC [ n B
  • Move the cursor down n lines.

If the screen is cleared, the terminal is asked to return the cursor to home and erase the display:

• CUP (Cursor position): ESC [ H
  • Move the cursor to upper left corner.
• ED (Erase display): ESC [ 2 J
  • Clear the entire screen.

Input sequences are read from the terminal, usually as a result of user input that isn't a simple character. Comlin supports the basic ESC [ and ESC O sequences for the arrow, Home, and End keys, and one extended sequence for the Delete key:

• ESC [ A: Up, like Ctrl-p
• ESC [ B: Down, like Ctrl-n
• ESC [ C: Right, like Ctrl-f
• ESC [ D: Left, like Ctrl-b
• ESC [ H or ESC O H: Home, like Ctrl-a
• ESC [ F or ESC O F: End, like Ctrl-e
• ESC [ 3 ~: Delete, like Ctrl-d

• Comlin is based on Linenoise

All credit for the original implementation goes to the authors of Linenoise. The history of this git repository preserves this lineage, but note that Comlin is a separate project with a completely incompatible API.