tmux-sync-split.sh (tss) script, spawn synchronized tmux panes with ssh or custom command

tmux-sync-split.sh

#!/bin/sh
################################################################################
#
# 2020-03-17 -- [email protected]
#
# Start a new synchronized 'N'-pane tmux session and run "$TSS_CMD $host" in
# each of the split window panes.
#
################################################################################
#
# Override variables:
#
#   TSS_CMD: run custom command in each pane, instead of 'ssh': supplies each
#       pane with a hostname from input list, unless.. (see: TSS_NOHOST)
#
#   TSS_LAYOUT: use some other predefined tmux layout, see tmux(1) manpage
#       for details (search "select-layout"), but common options are:
#       even-vertical, even-horizontal, tiled, main-vertical, main-horizontal
#
#   TSS_NOHOST: if set to any non-empty value, prevents input hosts from being
#       supplied as parameters to TSS_CMD: this parameter is useless without
#       also supplying some custom TSS_CMD.
#
################################################################################
#
# Other notes:
#
# Panes will remain in place after processes exit to collect output.
#
# Key bindings set by this script:
#
#    k      kill-session
#    =      toggle synchronize-panes
#
# Easiest way to exit after all panes are dead:
#    tmux escape char, then k
#    example: ^bk
#
################################################################################
#
# EXAMPLES
#
########################################
#
# Override TSS_CMD in your shell (for testing or otherwise) like so:
#
#   TSS_CMD=echo ./tmux-sync-split host1 host2 host3
#
# Override TSS_LAYOUT if you need/want tiled or horizontal splits like this:
#
#   TSS_LAYOUT=tiled ./tmux-sync-split host1 host2 host3
#
########################################
#
# Setup a 4-pane interactive shell 'dashboard'.  Can immediately turn off
# synchronize-panes and move between to run commands on local host.  Try
# using main-vertical or another predefined layout here as you prefer:
#
#   TSS_NOHOST=true TSS_LAYOUT=main-horizontal TSS_CMD=/bin/bash tss $(seq 1 3)
#
########################################
# Nightmare fuel test case:
#
# Spawn a 3x3 grid of synchronized panes running interactive local shell (bash);
# synchronization can be toggled for either rows or columns, and easy to get in
# a very awkward sync state:
#
#   TSS_NOHOST=true TSS_LAYOUT=even-horizontal TSS_CMD="TSS_NOHOST=true \
#     TSS_LAYOUT=even-vertical TSS_CMD=/bin/bash TMUX= tss 4 5 6" tss 1 2 3
#
################################################################################

# Set some defaults, allow overrides
TSS_CMD=${TSS_CMD:-ssh}
TSS_LAYOUT=${TSS_LAYOUT:-even-vertical}
TSS_OPTIONS=${TSS_OPTIONS:-"bind-key k kill-session\; bind-key = setw synchronize-panes\;"}

if [ -z "$2" ] && ! echo "$1" | grep ',' >/dev/null; then
    echo "Syntax: tmux-sync-split <host1,host2,host3,...|host1 host2 host3 ...>"
    exit 1
fi

host_list=""
if [ ! -z "$2" ] && ! echo "$1" | grep ',' >/dev/null; then
    host_list="$*"
else
    host_list=$(echo "$1" | sed 's/,/ /g')
fi

tmux_cmd=""
for host in ${host_list}; do
    # Reset default inner cmd on each loop to include input host
    inner_cmd_line="${TSS_CMD} ${host}"

    if [ -z "${tmux_cmd}" ]; then
        # If asked to avoid supplying input host..
        if [ ! -z "${TSS_NOHOST}" ]; then
            inner_cmd_line="${TSS_CMD}"
        fi

        #shellcheck disable=SC2089
        tmux_cmd="${TSS_OPTIONS}\; new-session '${inner_cmd_line} ; read'\; set remain-on-exit\;"
    else
        tmux_cmd="${tmux_cmd} split-window -v '${inner_cmd_line} ; read'\; select-layout ${TSS_LAYOUT}\;"
    fi
done

# already have a trailing semicolon here
tmux_cmd="${tmux_cmd} select-layout ${TSS_LAYOUT}\; set-window-option synchronize-panes"

eval tmux "${tmux_cmd}"