No AI. Build ed (the standard text editor) in 100 lines of C

ed text editor "ed is the standard text editor" Runs everywhere, even on a microwave Created by Ken Thompson in 1971 Used to write early Unix versions. Not TUI , pure CLI editor line-oriented editor Can be built using only C standard library — no termios, curses, or TUI dependencies. Present everywhere Works headless: runs via scripts/pipes without a human observer. AI love ed Evolution tree: ed - sed - ex - vi - vim. ** Note that final code contains several bugs ** `lines` array has not been initialized (`{0}`). `free lines` is missing the last line `strncpy(filename, path, sizeof(filename) - 1);` logic error when adding lines in 'a' (Append) mode. ** C is really difficult. **