Why the Post Steps and Post-build Actions are not executed after the build finished

My question is that The log file is in whole or in part when executed "post step" or "Post-build Actions". How to get the build result.

I want to get the build result,but there are no any plugins to get the result.So I did below this:

1 In my opinion,the "post step" are executed after the build finished. So I cofigured the job and selected "Run regardless of build result" at "post step" ,at the same time there is one bat at "execute windows at batch command".
The bat is used to query the two files "build.xml" and "log". But I can not find the string "<result>FAILURE</result>" in the "build.xml" and "Finished: FAILURE" in the file "log".
When the build finished,I queried these 2 files on the disk,the strings are exists in the two file.

2 I installed one plugin "Post build task" below "Post-build Actions",I put the string "FAILURE" into the Log text. but the Script did not executed.