CMake: Update man pages with addition only updates

Before this update the build system would not update generated man
pages in the folder `doc/man` if we only added lines to the source file
of the man page.

Author: sanssecours

doc/news/_preparation_next_release.md

@@ -308,7 +308,7 @@ you up to date with the multi-language support provided by Elektra.
 - The variable `ELEKTRA_STAT_ST_SIZE_F` now contains the correct format specifier for the `st_size` member of the `stat` struct on macOS. _(René Schwaiger)_
 - We simplified and unified the CMake code for the [Shell Tests](../../tests/shell) and the [Shell Recorder](../../tests/shell/shell_recorder). _(René Schwaiger)_
 - CMake now prints warnings about missing man pages. _(René Schwaiger)_
-- The build system now reverts man pages generated by `ronn`, if only the creation date of the man page changed. _(René Schwaiger)_
+- The build system does not update a man page in the folder [doc/man](../man) any more, if ronn only changed the creation date of the man page. _(René Schwaiger)_
 
 ### Compilation
 

scripts/cmake/ElektraManPage.cmake

@@ -25,19 +25,21 @@ endif (NOT EXISTS "${OLD_MAN_PAGE_COPY}")
 
 # We revert newly generated man pages, where only the date has changed.
 execute_process (COMMAND ${DIFF_COMMAND}
-			 -u
+			 -e
 			 ${MANPAGE}
 			 ${OLD_MAN_PAGE_COPY}
 		 OUTPUT_VARIABLE DIFF_OUTPUT)
-string (FIND "${DIFF_OUTPUT}" "\n+.TH" DIFF_POSITION_DATE_ADDED)
-string (FIND "${DIFF_OUTPUT}" "\n+" DIFF_LAST_POSITION_ADDED REVERSE)
+string (REGEX MATCH
+	      "^4c\n\\.TH [^\n]+\n\\.\n$"
+	      ONLY_DATE_CHANGED
+	      "${DIFF_OUTPUT}")
 
-if (NOT "${DIFF_POSITION_DATE_ADDED}" STREQUAL -1 AND "${DIFF_POSITION_DATE_ADDED}" STREQUAL "${DIFF_LAST_POSITION_ADDED}")
+if (NOT "${ONLY_DATE_CHANGED}" STREQUAL "")
 	execute_process (COMMAND ${CMAKE_COMMAND}
 				 -E
 				 copy
 				 ${OLD_MAN_PAGE_COPY}
 				 ${MANPAGE})
-endif (NOT "${DIFF_POSITION_DATE_ADDED}" STREQUAL -1 AND "${DIFF_POSITION_DATE_ADDED}" STREQUAL "${DIFF_LAST_POSITION_ADDED}")
+endif (NOT "${ONLY_DATE_CHANGED}" STREQUAL "")
 
 file (REMOVE "${OLD_MAN_PAGE_COPY}")