From 213e1a1ed6f75a541519e4030cc88ff851d6dd52 Mon Sep 17 00:00:00 2001
From: Daniel Naylor <daniel@ggim.me>
Date: Sun, 16 Jun 2024 19:04:08 +0100
Subject: [PATCH] Fixed bug relating to unsanitised pattern (#131)

---
 tex4ebook-exec_epub.lua | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/tex4ebook-exec_epub.lua b/tex4ebook-exec_epub.lua
index de07c19..a2faf6b 100644
--- a/tex4ebook-exec_epub.lua
+++ b/tex4ebook-exec_epub.lua
@@ -150,11 +150,18 @@ function remove_empty_guide(content)
   return content:gsub("<guide>%s*</guide>","")
 end
 
+local function startswith(str, prefix)
+  return str:sub(1, prefix:len()) == prefix
+end
+
 local function remove_builddir(filename)
   -- make4ht adds the build dir to all output files, 
   -- but we don't want them there, because it is appended to the outdir
   local builddir = Make.params.builddir
-  return filename:gsub("^" .. builddir .. "/", "")
+  if startswith(filename, builddir .. "/") then
+    return filename:sub((builddir .. "/"):len() + 1)
+  end
+  return filename
 end