README.md

@@ -10,10 +10,11 @@ The [check_folder_for_extension test folder](cffe_test) contains of 13 files, 12
 
 function call:
 ```
-check_folder_for_extension ./cffe_test "*.jpg *.JPG"
+check_folder ./cffe_test "*.jpg *.JPG"
 ```
 For multiple extensions (or other parts of the file name to match) space separate the list, like shown above.
 
+
 ## Clean up
 
 Cleaning up in a script and exit with a given exit code.
@@ -27,3 +28,34 @@ For testing the function call the script with:
 ```
 clean_up.sh test
 ```
+
+## Logger
+
+[Logger](logger.sh) to write messages with individual levels to a file. 
+
+In level *debug* all logged messages are printed to stdout, too.
+
+Log levels are 
+
+5 LLDebug,     *for exceptionally verbose messages, also on std out*
+
+4 LLInfo,      *informative messages*
+
+3 LLWarning,   *warning messages*
+
+2 LLError,     *error messages*
+
+1 LLMdtry and  *mandatory messages to get minimal info in a log file*
+
+0 LLMute       *really nothing gets written*
+
+The higher the level set in `$Log_Level` to the logger, the more verbose it gets.
+
+```
+logger $LLWARNING "This is my message";
+```
+produces the following message in the log file:
+
+```
+logger 20231122_22:43:19 Warning: This is my message!
+```