From <https://lists.gnu.org/archive/html/automake-patches/2015-07/msg00000.html>.
See also <http://bugs.gnu.org/22372>.

From 34163794a58b5bd91c5d6bd9adf5437571c7a479 Mon Sep 17 00:00:00 2001
From: Pavel Raiskup <praiskup@redhat.com>
Date: Tue, 7 Jul 2015 10:54:24 +0200
Subject: [PATCH] bin/automake: escape '{' in regexp pattern

Based on perlre(1) documentation:
.. in Perl v5.26, literal uses of a curly bracket will be required
to be escaped, say by preceding them with a backslash ("\{" ) or
enclosing them within square brackets ("[{]") ..

References:
https://bugzilla.redhat.com/1239379

* bin/automake.in (substitute_ac_subst_variables): Escape the
occurrence of '{' character.
---
 bin/automake.in | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/bin/automake.in b/bin/automake.in
index 0c29184..c294ced 100644
--- a/bin/automake.in
+++ b/bin/automake.in
@@ -3898,7 +3898,7 @@ sub substitute_ac_subst_variables_worker
 sub substitute_ac_subst_variables
 {
   my ($text) = @_;
-  $text =~ s/\${([^ \t=:+{}]+)}/substitute_ac_subst_variables_worker ($1)/ge;
+  $text =~ s/\$\{([^ \t=:+{}]+)}/substitute_ac_subst_variables_worker ($1)/ge;
   return $text;
 }
