GNU Screen – Using Terminal Escape Sequences

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I have a ruby terminal script that I would like to print out hyperlinks. I achieve that like so:

puts("\e]8;;https://example.com\aThis is a link\e]8;;\a")

This works perfectly fine in a "normal" terminal (gnome-terminal btw) window.

But I need to run this script within GNU screen, where the escape-sequence simply has no effect. Other sequences (like colors for example) work fine, the hyperlink one (which according to the source might be a gnome-terminal-only thing) doesn't. (screen is running inside gnome-terminal)

How can I get screen to acknowledge my link sequence and display it properly?

Best Answer

You can pass through some text to the terminal screen itself runs in by putting it inside an ESC P, ESC \ pair (\033P%s\033\\ in printf format).

So you should bracket inside \eP..\e\\ pairs all the parts of the sequence, except for the text which will appear on the screen ("This is a link"):

printf '\eP\e]8;;https://example.com\a\e\\This is a link\eP\e]8;;\a\e\\\n'
printf '\eP\e]8;;%s\a\e\\%s\eP\e]8;;\a\e\\\n' https://example.com 'This is a link'

Or, from C:

puts("\eP\e]8;;https://example.com\a\e\\This is a link\eP\e]8;;\a\e\\");
printf("\eP\e]8;;%s\a\e\\%s\eP\e]8;;\a\e\\\n", url, title);

Putting the replacement text too inside \eP..\e\\ may result in screen losing track of the cursor position.

This is documented in the GNU screen manual:

ESC P  (A)     Device Control String
               Outputs a string directly to the host
               terminal without interpretation

The "string" should should be terminated with a ST ("string terminator") escape, ie. \e\\ -- thence \eP..\e\\.

Related Solutions

Shell – Escape sequences in output of script called from ncurses application

The reason why an event-script fails to send a "growler" message is that mcabber closes the standard input, output and error streams when it runs an event command. You can see this in hooks.c:

  if ((pid=fork()) == -1) {
    scr_LogPrint(LPRINT_LOGNORM, "Fork error, cannot launch external command.");
    g_free(datafname);
    return;   
  }    
  if (pid == 0) { // child
    // Close standard file descriptors
    close(STDIN_FILENO);
    close(STDOUT_FILENO);
    close(STDERR_FILENO);
    if (execl(extcmd, extcmd, arg_type, arg_info, bjid, arg_data,
              (char *)NULL) == -1) {
      // scr_LogPrint(LPRINT_LOGNORM, "Cannot execute external command.");
      exit(1);
    }
  }
  g_free(datafname);

That makes the event script run without interfering with the streams used by mcabber.

There is no special ncurses mode intercepting the message (after all, tmux is already running as a terminfo application). You can probably work around the problem by redirecting your echo (preferably printf) to /dev/tty, e.g.,

#!/bin/sh
printf '\033Ptmux;\033\033]9;foobar\007\033\\' >/dev/tty

Bash – Non-printing escape sequence: when

The "non-printing escape sequence" is needed when using non-printing characters in $PS1 because bash needs to know the position of the cursor so that the screen can be updated correctly when you edit the command line. Bash does that by counting the number of characters in the $PS1 prompt and then that's the column number the cursor is in.

However, if you place non-printing sequences in $PS1, then that count is wrong and the line can be messed up if you edit the command line. Hence the introduction of the \[ and \] markers to indicate that the enclosed bytes should not be counted.

Best Answer

Related Solutions

Shell – Escape sequences in output of script called from ncurses application

Bash – Non-printing escape sequence: when

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