tmux: Support repeatable yank motions via yank.sh

Implementing logic inside tmux's config starts to become tedious with
growing complexity. Introduce a shell script that handles the logic of
the (now also repeatable) vim-like bindings.

.config/tmux/yank.sh

@@ -0,0 +1,54 @@
+#!/bin/sh
+
+get_var() {
+	tmux display-message -p "#{$1}"
+}
+
+command_prompt() {
+	tmux command-prompt -k -I "$2" -p "$1" 'display-message -p "%%"'
+}
+
+mode="$(get_var pane_mode)"
+if [ "$mode" != copy-mode ]; then
+	>&2 printf "%s: Not in copy mode\n" "$0"
+	exit 1
+fi
+
+# Just yank if we have a selection already
+selection_present="$(get_var selection_present)"
+if [ "$selection_present" -eq 1 ]; then
+	tmux send -X copy-pipe
+	exit 0
+fi
+
+# get motion
+motion="$(command_prompt "(operator-pending)")"
+
+# accumulate repeat number
+# NOTE: -N unfortunately does not work since the first non-numeric key press is
+#       lost then (TODO: is it really?)
+while printf "%s" "$motion" | grep -q '^[0-9]$'; do
+	repeat="$repeat$motion"
+	motion="$(command_prompt "(operator-pending-repeat)" "$repeat")"
+done
+# default to 1 if no repeat was specified
+: "${repeat:=1}"
+
+# abort on Escape
+[ "$motion" != "Escape" ] || exit 0
+
+# choose between character or line-wise selection
+case "$motion" in
+	y)
+		repeat="$((repeat - 1))"
+		motion="j"
+		tmux send -X select-line;;
+	j|k)
+		tmux send -X select-line;;
+	*)
+		tmux send -X begin-selection;;
+esac
+
+# move and yank
+[ "$repeat" -eq 0 ] || tmux send -N "$repeat" "$motion"
+tmux send -X copy-pipe