From 80f464d9d72839841422f75e78ce725365cc3d71 Mon Sep 17 00:00:00 2001
From: Mateusz Piotrowski <0mp@FreeBSD.org>
Date: Wed, 9 Jan 2019 14:45:00 +0100
Subject: [PATCH] Escape square brackets in configure.ac

This patch attempts to solve the regression introduced in e8b0efdc
(#2607).
---
 configure.ac | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index 4f00ff014..55600d90b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -275,7 +275,7 @@ test "$prefix" = NONE && prefix=$ac_default_prefix
 test "$exec_prefix" = NONE && exec_prefix='${prefix}'
 for name in $ac_subst_vars; do
     for _ in 1 2 3; do
-    if printf '%s' "${name}" | egrep '^[_[:alpha:]][_[:alnum:]]*$'
+    if printf '%s' "${name}" | egrep '^[[_[[:alpha:]]]][[_[[:alnum:]]]]*$'
     then
         eval "${name}"="$(eval echo "\${${name}}")"
     fi