Bash completion patch to fix error in expr

--- a/scripts/generate_bash_completion.sh.orig
+++ a/scripts/generate_bash_completion.sh
@@ -34,7 +34,7 @@
 }
 
 get_optarg() {
-  expr -- "${1}" : "[^=]*=\\(.*\\)"
+  expr "${1}" : "[^=]*=\\(.*\\)"
 }
 
 append=