Rename the tmux or iTerm2 window when connecting to a remote host

Daniel Kertesz included in Tips and Tricks

2019-12-13 557 words 3 minutes

Contents

Info

This is an updated version of one of my old posts.

The following zsh code wraps the ssh command to grab the remote hostname, shorten it as needed and use it to rename the current tmux or iTerm2 window or pane. It’s really handy when you connect to several different servers at once.

Warning

This function have a subtle but annoying bug: launching ssh without any argument will cause the current terminal window to close. It took me a while to notice, because generally I would always execute ssh to connect to something…

# ssh wrapper function to set tmux window (pane?) title

# bypass this function if stdout is not a terminal, to avoid messing up
# the output with our printf() calls.
[[ -t 1 ]] || exec command ssh $@

local prev_window_name=$(tmux display-message -p "#{window_name}")
local prev_pane_title=$(tmux display-message -p "#{pane_title}")

local win_escape_start="\033k"
local pane_escape_start="\033]2;"
local escape_end="\033\\"

set_pane_title() {
    printf "$pane_escape_start$1$escape_end"
}

set_window_title() {
    printf "$win_escape_start$1$escape_end"
}

local hostname=$(ssh -G "$@" | awk 'NR > 2 { exit } /^hostname/ { print $2 }')

if [[ -z $hostname ]]; then
    command ssh $@
else
    # try to shorten the hostname

    # 1) split the hostname on "."
    local parts=(${(s:.:)hostname})
    local short_name

    # 2) if the parts of the hostname are less than 3 (e.g. mail.example.com -> 3 parts)
    # use the first part only (e.g. "mail")
    if (( $#parts <= 3 )); then
        short_name=${parts[1]}
    else
        # othewrise show 2/3 of the hostname
        local fraction=$(( $#parts / 3 * 2 ))
        short_name=${(j:.:)parts[1,$fraction]}
    fi
    # Set window name and pane title when there's only 1 pane (i.e. the whole window),
    # otherwise set just the pane title.
    if [[ $(tmux display-message -p "#{window_panes}") == 1 ]]; then
        # Use a shortened version of the hostname for the window title
        tmux rename-window "$short_name"
        set_pane_title $hostname
    else
        set_pane_title $hostname
    fi
    command ssh $@

    # Restore the old window and pane titles after ssh exits.
    if [[ $(tmux display-message -p "#{window_panes}") == 1 ]]; then
        tmux rename-window "$prev_window_name"
        tmux setw automatic-rename on
    fi
    set_pane_title $prev_pane_title
fi

A really nice trick that I found somewhere and modified to my own needs is used to get the canonical hostname of the remote server I’m connecting to using OpenSSH:

local hostname=$(ssh -G "$@" | awk 'NR > 2 { exit } /^hostname/ { print $2 }')

Running ssh -G <hostname> will print the full OpenSSH configuration for that hostname, which includes a single Hostname <address> line containing the actual hostname of the remote server (in casey you’re using aliases); the awk incantation will match the line starting with hostname, print the second element of that line and exit after the 2nd line of output (this is because the hostname statement has been, so far, the second line of the output).

I put this file in one of my zsh $fpath directories and autoload it from ~/.zshrc:

typeset -U fpath
fpath+=~/Preferences/zsh/functions
autoload -Uz ssh

To do the same thing when running iTerm2 without tmux, you can remove all the lines invoking the tmux command and replace the set window title with something like:

set_window_title() {
    echo -ne "\033]0;"$1"\007"
}

And to restore the default window title when ssh exits, you can just invoke set_window_title passing an empty string, like set_window_title "".

This code can also be found on Github in my dotfiles repo.