Add script for spawning alacritty in CWD

The script uses the recently added _NET_WM_PID window property for
finding the program running in Alacritty, fetching its working
directory, and spawning a new Alacritty using that directory.

scripts/spawn-alacritty-cwd

@@ -0,0 +1,44 @@
+#!/bin/bash
+
+# Spawn a new instance of Alacritty using the CWD of the currently focused
+# Alacritty process.
+#
+# This is useful in environment like i3 where terminals are opened using a
+# key-combination while another terminal is already focused.
+#
+# If the script is run with a non-Alacritty window in focus or a non-compliant
+# version of Alacritty, the script will exit with code 1. This makes it possible
+# to use the script like
+#
+#     spawn-alacritty-cwd || alacritty
+#
+
+ACTIVE_WINDOW=$(xdotool getactivewindow)
+ACTIVE_WM_CLASS=$(xprop -id $ACTIVE_WINDOW | grep WM_CLASS)
+
+if [[ $ACTIVE_WM_CLASS == *"Alacritty"* ]]
+then
+    # Get PID. If _NET_WM_PID isn't set, bail.
+    PID=$(xprop -id $ACTIVE_WINDOW | grep _NET_WM_PID | grep -oP "\d+")
+    if [[ "$PID" == "" ]]
+    then
+        exit 1
+    fi
+
+    # Get first child of terminal
+    CHILD_PID=$(pgrep -P $PID)
+    if [[ "$PID" == "" ]]
+    then
+        exit 1
+    fi
+
+    # Get current directory of child. The first child should be the shell.
+    pushd "/proc/${CHILD_PID}/cwd"
+    SHELL_CWD=$(pwd -P)
+    popd
+
+    # Start alacritty with the working directory
+    alacritty --working-directory $SHELL_CWD
+else
+    exit 1
+fi