From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Mon, 13 Dec 2021 20:40:37 +0000 (-0700)
Subject: Use one instead of two regexes.
X-Git-Tag: v9.4.0-rc1~732^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F13071%2Fhead;p=dealii.git

Use one instead of two regexes.
---

diff --git a/doc/doxygen/scripts/filter b/doc/doxygen/scripts/filter
index cb4757b44e..b8c293c8dd 100755
--- a/doc/doxygen/scripts/filter
+++ b/doc/doxygen/scripts/filter
@@ -26,11 +26,11 @@ while (<>)
     ########################################################
 
 
-    # make sure we can just write $...$ for formulas.
-    s/\$/\@f\$/g;
-
-    # however, undo that change if the dollar sign was escaped with a backslash
-    s/\\\@f\$/\$/g;
+    # Make sure we can just write $...$ for formulas, except if
+    # the dollar sign was escaped with a backslash (use negative
+    # look-behind to detect that case, using (?<!\\) to make sure
+    # the preceding character -- if there is any -- is not a backslash):
+    s#(?<!\\)\$#\@f\$#g;
 
     # We don't let doxygen put everything into a namespace
     # dealii. consequently, doxygen can't link references that contain an