Ctrl+L vs clear

In a terminal, you can clear the screen in two common ways:

• Run the clear command
• Press Ctrl+L

The result looks the same at first, but there’s a catch: clear can also wipe your scrollback buffer¹, while Ctrl+L never does. Also, behind the scenes they’re implemented in different ways.

Ctrl+L

When you press Ctrl+L at the Bash prompt, it’s not invoking an external program, but instead it’s handled inside GNU Readline, the library Bash uses for interactive line editing². In Readline’s input keymap, the key Ctrl+L is bound to the clear-screen function. You can confirm this with:

bind -P | grep clear-screen

which shows:

clear-screen can be found on "\C-l".

The function name “clear-screen” is registered in funmap.c:

{ "clear-screen", rl_clear_screen },

The actual function rl_clear_screen() is defined in text.c. It calls the helper function _rl_clear_screen(), defined in display.c, which eventually calls:

tputs(_rl_term_clrpag, 1, _rl_output_character_function);

Here _rl_term_clrpag is a global char * set up in terminal.c. At startup, Readline queries terminfo(5)³, and assigns to _rl_term_clrpag the value of the “clear” capability (short code “cl”)⁴. On a terminal with $TERM set to xterm-256color, that expands to:

\E[H\E[2J

which means:

• ESC[H → move the cursor to the home position (row 1, column 1)
• ESC[2J → erase the entire screen

You can see this mapping yourself with:

infocmp -C $TERM | grep 'cl='

So Ctrl+L sends ESC[H ESC[2J, clears the visible screen, and redraws the prompt, but scrollback remains intact.

clear(1)

When you run the clear(1) command, you’re executing a program provided by ncurses. Like Ctrl+L, it looks up the “clear” capability in terminfo(5) and prints the corresponding escape sequence. But clear goes a step further: unless you pass -x, it also checks for the extended capability E3, which on xterm is defined as:

E3=\E[3J

which tells the terminal to erase the scrollback buffer. That’s the key difference.

Here’s the relevant code from clear.c, which calls clear_cmd.c:

int
clear_cmd(bool legacy)
{
    int retval = tputs(clear_screen, lines > 0 ? lines : 1, putch);
    if (!legacy) {
	/* Clear the scrollback buffer if possible. */
	char *E3 = tigetstr("E3");
	if (E3)
	    (void) tputs(E3, lines > 0 ? lines : 1, putch);
    }
    return retval;
}

where:

• clear_screen is a macro defined in term.h, and after setupterm() initializes the terminal entry, it expands to the string for the “clear” capability ( on xterm-256color that’s \E[H\E[2J).
• The second part (tigetstr("E3")) is what makes clear different from Ctrl+L: if defined, it sends \E[3J to erase scrollback.

So on an xterm-like terminal:

• clear = ESC[H ESC[2J ESC[3J → clears screen and scrollback
• clear -x = ESC[H ESC[2J → same as Ctrl+L

You can try it directly:

echo -e "\033[H\033[2J"        # clear only (Ctrl+L / clear -x)
echo -e "\033[H\033[2J\033[3J" # clear + erase scrollback (clear)

In short, Ctrl+L and clear -x both just reset the visible screen, while plain clear also erases the scrollback.