The easiest way to clear scrollback buffer of terminal + some deeper explanation

escape-charactersreadlinetermcapterminal-emulatorterminfo

Why bother?

Clearing scrollback buffer is handy in many ways, for example, when I wish to run some command with long output, and want to quickly scroll to start of this output. When scrollback buffer is cleared, I can just scroll to top, and will be done.

Some considerations:

There is clear command, according to man,

clear clears your screen if this is possible, including its scrollback buffer (if the extended "E3" capability is defined).

In gnome-terminal clear does not clear scrollback buffer. (What is "E3" capability, though?)

There is also reset, which clears, but it does a little bit more than that, and it is really slow (on my system it takes more than a second, which is significant delay for humans to be noticed).

And there is echo -ne '\ec' or echo -ne '\033c', which does the job. And indeed it is much faster than reset.

The question is, what is \ec sequence, how it differs from what clear and reset does, and why there is no separate command for it?

There is also readline's C-l key sequence, which by default bound to clear-screen command (I mean, readline command, not shell command). What is this command? Which escape sequence it emits? How does it actually work? Does it run shell command? Or what? Again, in gnome-terminal, it seems like it works just by spiting out blank lines until prompt appear in top line of terminal. Not sure about other terminal emulators. This is very cumbersome behavior. It pollutes scrollback with chunks of emptiness, so you must scroll up more, and more. It is like a hack, rather than clean solution.

Another question is, is there a readline command for mentioned \ec sequence? I want to bound it to C-l instead because I always want to clear scrollback buffer when I clear the screen.

And another question is how to just type such escape sequence into terminal, to perform desired action? Then do not have to think about binding C-l to another readline command (if such command exists). I tried typing Esc, then c but this does not work.

UPDATE
This question answered mostly here: https://unix.stackexchange.com/a/375784/257159. It is very good answer which explains almost all questions asked here.

Best Answer

Many terminal emulators use the same escape sequences as XTerm, or similar. For XTerm, Escc is defined as "Full Reset (RIS)". It seems reasonable that a full reset would clear the scrollback buffer.

I have had no success using readline to bind to the sequence itself, but a workaround is

bind '"\C-l": "\C-a\C-kprintf\ "\\033c"\C-m"'

This has some caveats. First, it puts the printf command in your shell history, which is not ideal. Second, it cannot be used while inputting a command; it overwrites the current input line.

Related Solutions

Bash – Bind C-i and TAB keys to different commands in terminal applications via .inputrc

The terminal emulator translates events like “the Tab key was pressed” into sequences of characters that the application running in the terminal (bash, in your case) reads. See How do keyboard input and text output work? for a more detailed presentation of this topic.

For historical reasons, a few of keys send a character that's the same as pressing Ctrl with some other character: Tab = Ctrl+I, Return = Ctrl+M, Esc = Ctrl+[. This is because historical physical terminals did this, so applications that run in terminals expect it, so terminals do it.

Both Guake and Gnome-terminal use the VTE library, which does not allow the mapping from key chords to character sequences to be configured. You have the same problem as bash - wrong key sequence bindings with control+alt+space

Xterm has fully configurable key bindings. You can make the Tab key send a tab character (that's the default), or make it send the string hello, or whatever you choose. Xterm is configured via X resources. For example, to make Tab send the escape sequence \e[t when pressed and \e]t when released, put this in your ~/.Xresources:

XTerm.vt100.translations: #override \
  <Key>Tab: string("\033[t") \n\
  <KeyRelease>Tab: string("\033]t") \n\

Or maybe you would leave Tab sending the tab character and make Ctrl+I send something else:

XTerm.vt100.translations: #override \
  Ctrl~Meta~Shift<Key>I: string("\033[a5i") \n\
  Ctrl~Meta Shift<Key>I: string("\033[a6i") \n\

You can then bind \e[a5i to whatever you want in bash and other terminal applications with configurable keybindings.

Note that by convention, multi-character escape sequences start with the escape character (often represented as \e or \033 or \x1b in programming languages and configuration files); some applications may have trouble with escape sequences starting with other characters, and of course you can't have a character that's both an escape sequence and a key of its own, unless you're willing to accept a timeout (that's how it works in applications such as vi where Esc on its own is bound to some functionality). If you define your own key sequences, take care not to clash with the ones sent by function and cursor keys, which are more or less de facto standardized.

Bash – Readline: Binding an ANSI escape sequence to a key

Two parts:

bash lets you bind a key to the readline clear-screen function (which seems to be the original goal).
in bash, readline's purpose is to prepare text (by editing, etc) for issuing commands to bash. An escape sequence would be sent to the terminal. None of the listed functions for readline would act as a replacement for echo or printf.

Key bindings for readline expect a single function-name or literal string. In your example, readline read what it considered a possible function name, and ignored the rest of the line.

So: no, bash/readline provide no useful features for echoing an escape sequence directly as a key-binding. You have to go another level, as noted, using echo.

Best Answer

Related Solutions

Bash – Bind C-i and TAB keys to different commands in terminal applications via .inputrc

Bash – Readline: Binding an ANSI escape sequence to a key

Related Question