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I have Mouse mode set to on in Tmux so that I can make use of the scroll wheel using set-window-option -g mode-mouse on.

However if I want to copy the output of a particular command which spans more than the height of the terminal window, I can't scroll down while holding the shift key.

What modifications do I need to make to the configuration file in order to get the desired behavior?

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Probably you cannot. xterm (and the programs which act like it) makes a distinction between mouse operations with/without the shift modifier:

  • the unshifted operations can be programmed, i.e., an application can send an escape sequence telling xterm to send back escape sequences for each mouse click.
  • the unshifted operations cannot be programmed in this way. They are left as-is.

So tmux is not likely to be able to change this behavior. Further, the way the mouse buttons are used is (again, an old convention) in the way: one button acts to start a selection, another to extend the selection and the third to paste the selection. Some terminals may implement dragging if you hold down the extend-selection button.

But the wheel mouse is (really) much newer than the rest of the protocol, probably from the mid/late-1990s. In the mouse protocol, it sends fake button events, e.g., buttons 4 and 5. While a terminal could be implemented to extend a selection using the wheel mouse, tmux has no way to control that—and it likely would be built-in/not-configurable. If you are not seeing the desired behavior already, you probably cannot get it.

The distinction with shift is very old, and not confined to mouse operations: on some platforms, the page-up and page-down keys are setup to scroll the terminal when the shift modifier is added, while the unshifted keys may be read from an application.

Further reading:

  • Wheel mice (XTerm Control Sequences)
  • Normal tracking mode (XTerm Control Sequences)
  • Default Key Bindings XTerm manual, e.g., the bindings for mouse-buttons

                       ~Meta <Btn1Down>:select-start() \n\
                     ~Meta <Btn1Motion>:select-extend() \n\
                   ~Ctrl ~Meta <Btn2Up>:insert-selection(SELECT, CUT_BUFFER0) \n\
                 ~Ctrl ~Meta <Btn3Down>:start-extend() \n\
                     ~Meta <Btn3Motion>:select-extend() \n\
    
  • Thank you for the explanation. I would like to add that having set -g terminal-overrides 'xterm*:smcup@:rmcup@' in the config file gave me what I was looking for but at the cost of some keyboard functionality. Like I couldn't use arrow keys or page up page down keys with it and scrolling long text with mouse is a bit tedious so I went back with the defaults. – Ashesh Kumar Singh Jan 28 '16 at 19:28

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