[ADD][SCRIPTS] i3-get-window-criteria script

This makes it easier to write an i3 filter command, by just executing
the script and clicking on the window you want to filter.

scripts/i3-get-window-criteria

@@ -0,0 +1,40 @@
+#!/bin/sh
+
+# i3-get-window-criteria - Get criteria for use with i3 config commands
+
+# To use, run this script, then click on a window.
+# Output is in the format: [<name>=<value> <name>=<value> ...]
+
+# Known problem: when WM_NAME is used as fallback for the 'title="<string>"' criterion,
+# quotes in "<string>" are not escaped properly. This is a problem with the output of `xprop`,
+# reported upstream: https://bugs.freedesktop.org/show_bug.cgi?id=66807
+
+PROGNAME=$(basename "$0")
+
+# Check for xwininfo and xprop
+for cmd in xwininfo xprop; do
+    if ! command -v $cmd > /dev/null 2>&1; then
+        echo "$PROGNAME: $cmd: command not found" >&2
+        exit 1
+    fi
+done
+
+match_int='[0-9][0-9]*'
+match_string='".*"'
+match_qstring='"[^"\\]*(\\.[^"\\]*)*"' # NOTE: Adds 1 backreference
+
+{
+    # Run xwininfo, get window id
+    window_id=$(xwininfo -int | sed -nre "s/^xwininfo: Window id: ($match_int) .*$/\1/p")
+    echo "id=$window_id"
+
+    # Run xprop, transform its output into i3 criteria. Handle fallback to
+    # WM_NAME when _NET_WM_NAME isn't set
+    xprop 8u -id "$window_id" |
+        sed -nr \
+            -e "s/^WM_CLASS\(STRING\) = ($match_qstring), ($match_qstring)$/instance=\1\nclass=\3/p" \
+            -e "s/^WM_WINDOW_ROLE\(STRING\) = ($match_qstring)$/window_role=\1/p" \
+            -e "/^WM_NAME\(STRING\) = ($match_string)$/{s//title=\1/; h}" \
+            -e "/^_NET_WM_NAME\(UTF8_STRING\) = ($match_qstring)$/{s//title=\1/; h}" \
+            -e '${g; p}'
+} | sort | tr "\n" " " | sed -r 's/^(.*) $/[\1]\n/'