+# While pre-processing if version is set to "search" look for a version string
+# in the following file.
+pre && version == "search" && version_file == ""{
+ version_file = FILENAME
+}
+
+pre && version == "search" && version_file != FILENAME{
+ print "version string not found in", version_file
+ err = 1
+ exit 1
+}
+
+pre && version == "search" && $0 ~ /^ \* libpng version/{
+ version = substr($0, 4)
+ print "version =", version >out
+ next
+}
+
+pre && FILENAME == version_file{
+ next
+}
+