Tag Archives: mode

Vi mode in tmux

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Updated May 2017 to show the new syntax for the copy-mode keys.

tmux offers a set of vi-like bindings for navigating a buffer in a window. These allow you to not only navigate through the buffer beyond what your screen is currently showing, but also to search all the output generated thus far, and to select and copy text that can be pasted in any other window in the tmux session.

You can enable this as a default setting in .tmux.conf with the following:

set-window-option -g mode-keys vi

You can confirm this is working by pressing Ctrl+B and then : in a tmux session to bring up the command line, and typing:

list-keys -T copy-mode-vi

In version 2.3 and below, the syntax is different:

list-keys -t vi-copy

This will bring up a complete list of the vi-like functionality available to you in this mode.

With this done, within a tmux instance, pressing Ctrl+B and then [ will enter copy mode, allowing you to copy text or view the history of the buffer, including searching with / and ?. Most of the basic vi movements work, including screenwise vertical movement commands like Ctrl+F and Ctrl+B. You can leave this mode just by pressing Enter, or you can start a selection by pressing Space on a character, moving to another, and then pressing Enter. If you have text copied like this you can paste it into any tmux window in that session by pressing Ctrl+B and then ].

If you don’t mind artifically introducing a few Vim-only features to the vi mode, you can set things up so that v starts a selection and y finishes it in the same way that Space and Enter do, more like Vim:

bind-key -T copy-mode-vi 'v' send -X begin-selection
bind-key -T copy-mode-vi 'y' send -X copy-selection-and-cancel

In version 2.3 and below, the syntax is very different:

bind-key -t vi-copy 'v' begin-selection
bind-key -t vi-copy 'y' copy-selection

Even if you’re using a terminal emulator in a GUI environment, if you get good at using this you’ll find it’s much faster and more precise than clicking and dragging to select text to copy and paste it. It keeps you from having to move to the mouse, and additionally eliminates the problem of copying whole lines split into more than one panes.

Note that all of the above assumes that your prefix is the default of Ctrl+B, which many tmux users, myself included, seem to prefer to change to the old GNU Screen prefix key of Ctrl+A.

Vi mode in Bash

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Because the Bash shell uses GNU Readline, you’re able to set options in .bashrc and .inputrc to extensively customise how you enter your command lines, including specifying whether you want the default Emacs-like keybindings (e.g. Ctrl+W to erase a word), or bindings using a modal interface familiar to vi users.

To use vi mode in Bash and any other tool that uses GNU Readline, such as the MySQL command line, you need only put this into your .inputrc file, then log out and in again:

set editing-mode vi

If you only want to use this mode in Bash, an alternative is to use the following in your .bashrc, again with a login/logout or resourcing of the file:

set -o vi

You can check this has applied correctly with the following, which will spit out a list of the currently available bindings for a set of fixed possible actions for text:

$ bind -P

The other possible value for editing-mode is emacs. Both options simply change settings in the output of bind -P above.

This done, you should find that you open a command line in insert mode, but when you press Escape or Ctrl+[, you will enter an emulation of Vi’s normal mode. Enter will run the command in its present state while in either mode. The bindings of most use in this mode are the classic keys for moving to positions on a line:

  • ^ — Move to start of line
  • $ — Move to end of line
  • b — Move back a word
  • w — Move forward a word
  • e — Move to the end of the next word

Deleting, yanking, and pasting all work too. Also note that k and j in normal mode allow you to iterate through your history in the same way that Ctrl+P and Ctrl+N do in Emacs mode. Searching with ? and / doesn’t work by default, but the Ctrl+R and Ctrl+S bindings still seem to work.

If you are reasonably used to working with the modeless Emacs for most of your shell work but do occasionally find yourself in a situation where being able to edit a long command line in vi would be handy, you may prefer to press Ctrl+X Ctrl+E to bring up the command line in your $EDITOR instead, affording you the complete power of Vim to edit rather than the somewhat sparse vi emulation provided by Readline. If you want to edit a command you just submitted, the fc (fix command) Bash builtin works too.

The shell is a very different environment for editing text, being inherently interactive and fixed to one line rather than a static multi-line buffer, which leads some otherwise diehard vi users such as myself to prefer the Emacs mode for editing commands. For one thing, vi mode in Bash trips on the vi anti-pattern of putting you in insert mode by default, and at the start of every command line. But if the basic vi commands are etched indelibly into your memory and have become automatic, you may appreciate being able to edit your command line using these keys instead. It’s certainly worth a try at any rate, and I do still occasionally see set -o vi in the .bashrc files of a few of the pros on GitHub.

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Command line editing

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By default, the Bash shell uses GNU Readline, which provides a set of Emacs-friendly key bindings that are a pretty workable way to edit long and complicated commands. If you learn a little about the chords available to you in editing Bash commands through this library, and combine that with a little old-school command-line magic, you can work at high speed with decent accuracy quite easily. Alternatively, if you don’t like the Emacs-style keybindings and would prefer to stick to a vi-friendly model, you can use set -o vi to edit your command line directly with vi keybindings.

However, if you’re building a particularly complex string of commands involving a lot of pipes, escapes, and redirections, it often turns out to be handy to actually load them into your favourite editor, to give you full facility to edit them in any way you wish. Bash provides a method for this in the form of its Ctrl+X, Ctrl+E binding.

To use it, you can type anything at the command prompt (including nothing at all) and press Ctrl+X, Ctrl+E to bring up your EDITOR, be it Vim, Emacs, or Nano, with the contents of the command line there to edit. As soon as you save and quit, the command will be run as stated, and will be entered into the command history as if you typed it out on the shell directly.

There’s also a handy built-in Bash shortcut, fc (short for “fix command”) to open the previous command in your editor, allow you to edit it, and then run it automatically when you quit. This is particularly useful if you’ve made a small mistake in a complex line of shell code.

If this happens to bring up the wrong editor, perhaps because your choice doesn’t match that of the system administrator, you can set your personal preference of editor like so:

$ export EDITOR=/usr/bin/vim

You can confirm this is working by checking your environment variables:

$ env

One downside of this method is that without special setup within your editor, you lose some of the benefits of things like tab completion. Fortunately it only takes a little creative mapping to make this work in Vim, taking advantage of the Ctrl+X, Ctrl+F file completion that’s already built in. You could even bind that straight to the Tab key if you don’t otherwise use it.

:inoremap <Tab> <C-X><C-F>