added dependency check for rg

check_licenses.sh

@@ -1,4 +1,12 @@
 #!/bin/sh
-# Depends on: `rg` (ripgrep)
 
-! rg --multiline --files-without-match --glob '*.rs' --pcre2  '(?<!\n)((//)|(#)) Copyright \(c\) \d+ [A-z, ]+\n((//)|(#)) SPDX-License-Identifier: .*\n'
+set -e
+
+# check if we have rg(1)
+if ! command -v rg >/dev/null 2>&1; then
+	printf "%s: Missing dependency: rg(1)\n" "$0" 1>&2
+	exit 71 # sysexits(3) EX_OSERR
+else
+	rg --multiline --files-without-match --glob '*.rs' --pcre2 \
+		'(?<!\n)((//)|(#)) Copyright \(c\) \d+ [A-z, ]+\n((//)|(#)) SPDX-License-Identifier: .*\n'
+fi