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~2 min readDisplay & Input

Terminal Raw Mode

By default, the terminal is in cooked mode: it line-buffers input, echoes typed characters, intercepts Ctrl+C/Ctrl+Z, and translates \r to \n. Great for shell scripts. Terrible for an editor — you want to react to every single keystroke the moment it happens.

Every serious terminal editor flips the same set of bits in termios:

struct termios raw = orig;
raw.c_iflag &= ~(BRKINT | ICRNL | INPCK | ISTRIP | IXON);
raw.c_oflag &= ~(OPOST);
raw.c_cflag |=  (CS8);
raw.c_lflag &= ~(ECHO | ICANON | IEXTEN | ISIG);
tcsetattr(STDIN_FILENO, TCSAFLUSH, &raw);

What each flag does, and why we kill it:

Flag	Field	Meaning	Why disable
`ECHO`	lflag	Echo typed chars	We render the buffer ourselves
`ICANON`	lflag	Line buffering	We want chars, not lines
`ISIG`	lflag	Ctrl+C, Ctrl+Z → signals	We want Ctrl+C as a key
`IEXTEN`	lflag	Ctrl+V literal-next	Avoid double-key consumption
`IXON`	iflag	Ctrl+S, Ctrl+Q flow control	We want those as keys
`ICRNL`	iflag	`\r` → `\n` translation	We want raw `\r`
`OPOST`	oflag	Output `\n` → `\r\n` translation	We emit `\r\n` ourselves
`BRKINT`, `INPCK`, `ISTRIP`	iflag	Legacy 7-bit serial cruft	Modern hygiene
`CS8`	cflag	8-bit chars	Required for UTF-8

Always save the original termios and restore it on exit (atexit, or RAII in C++/Rust). If your editor crashes without restoring, the user's shell is left in raw mode — broken until they reset.

This lesson simulates the bit manipulation so you can verify which flags are cleared without needing an actual terminal. The same mental model carries to Windows console mode (SetConsoleMode with ENABLE_VIRTUAL_TERMINAL_INPUT) and to UI toolkits like crossterm (Rust), tcell (Go), prompt_toolkit (Python).

Reference: termios(3), kilo enableRawMode(), Hecto chapter 2.

next: Practice

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