Nerdy Weekly

Musings on the joy of computing... or lack thereof



Enable italic text inside vim inside tmux inside gnome-terminal

Update: As egmont pointed out in the comments: setting TERM=xterm inside tmux is discouraged and will cause wrong behavior in some programs. Changing all instances of xterm-256color to screen-256color in this tutorial should work, but I’m no longer using gnome-terminal so I can’t test that. I’m now a KDE convert by the way; italic text Just Workstm with Konsole. Neat, eh?

It has bothered me for a while what I can’t get terminal vim to display italic text. It might seem trivial but it makes a world of difference when I’m editing Markdown or HTML. Here’s what gvim looks like:

Neat, right? This is what terminal vim shows:

I don’t know about you, but the second one looks catastrophically messy and counterintuitive to me. Let’s change that. My current setup is terminal vim running inside a tmux session on gnome-terminal. Let’s go through these things.

gnome-terminal

Note that older versions of gnome-terminal do not support italic text. To check if your terminal does support it, run this command:

$ echo -e "\e[3m foo \e[23m"

If your version of gnome-terminal supports it, an italic foo will appear. If not, upgrade it! :)

vim

You may have noticed: [3m and [23m are the special sequences to start and stop printing italic text. Unfortunately, vim doesn’t care about those. It expects sitm and ritm instead. We’ll need to map them manually. Simply use these commands:

# Download a custom terminfo that defines sitm and ritm
$ wget https://gist.githubusercontent.com/sos4nt/3187620/raw/8e13c1fec5b72d415ed2917590348451de5f8e58/xterm-256color-italic.terminfo
# Compile it
$ tic xterm-256color-italic.terminfo
# Activate xterm-256color-italic.terminfo automatically
# (edit filename accordingly if you're using another shell)
$ echo 'export TERM=xterm-256color-italic' >> ~/.bashrc

Open a new terminal window and try the first command again. You should now see an italic foo. If not, I can’t help you any further :P

tmux

The only reason I use terminal vim instead of gvim is tmux integration, therefore I almost always run vim inside a tmux session. Unfortunately tmux does some weird things to your terminal, one of them is altering the $TERM environment variable. When we open a tmux session, it will typically reset $TERM to screen-256color or something like that.

If you did the previous step, the export command in your .bashrc should have overridden tmux’s $TERM value. If for some reason it doesn’t work, you can directly tell tmux to use the correct value. Add this line to ~/.tmux.conf:

set -g default-terminal "xterm-256color-italic"

More on vim

If you still can’t see any italic text in a markdown file, it might be because your colorscheme deliberately disables it. Try using another colorscheme (I highly recommend solarized). You can also check if your markdown syntax plugin does use italics; I’m currently using Tim Pope’s markdown plugin and it works great!

References:

  1. Terminal that supports ANSI italic escape code?
  2. gnome-terminal’s italic escape codes
  3. Enabling italic fonts in iTerm2, tmux, and vim

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