01-3-Logging-Script.md

📘 Logging Script Output in Batch Scripting

• Debugging: Helps identify where and why a script failed
• Auditing: Keep a record of actions taken by automated jobs
• Monitoring: Send logs to IT teams or systems

🔹 Basic Logging Techniques

1. 📥 Redirect All Output to a File

   @ECHO OFF
   REM Redirect stdout and stderr to log.txt
   MYCOMMAND > log.txt 2>&1

   This captures everything the command prints (success or error).

2. 📒 Append Instead of Overwrite

   Use >> instead of > to preserve previous log content:

   @ECHO OFF
   ECHO Starting task... >> log.txt
   MYCOMMAND >> log.txt 2>&1
   ECHO Task completed. >> log.txt

---

1. Logging the Entire Script

   Wrap your entire script in a block and redirect it:

   @ECHO OFF
   (
   ECHO ===== Script Started at %DATE% %TIME% =====
   DIR C:\SomeFolder
   XCOPY C:\Data D:\Backup /E /I
   ECHO ===== Script Finished at %DATE% %TIME% =====
   ) >> script.log 2>&1

2. Add Timestamps to Each Log Entry

   Use this format to prepend a timestamp to each log message:

   @ECHO OFF
   SET LOGFILE=script.log
   
   CALL :Log "Script started"
   DIR "C:\Fake\Path" >> %LOGFILE% 2>&1
   CALL :Log "Completed directory check"
   GOTO :EOF
   
   :Log
   ECHO [%DATE% %TIME%] %~1 >> %LOGFILE%
   EXIT /B

   🔁 You can reuse :Log throughout the script to make logging consistent.

3. Separate Output and Error Logs

   Sometimes it's useful to keep clean logs:

   MYCOMMAND > output.log 2> error.log

   This allows you to parse success and failure info independently.

4. Rotating Logs (Simple Method)

   Prevent log files from growing indefinitely:

   @ECHO OFF
   SET LOGFILE=script.log
   
   IF EXIST %LOGFILE% (
   REN %LOGFILE% script_%DATE:/=_%_%TIME::=_%.log
   )
   
   ECHO [LOG] New log started at %DATE% %TIME% > %LOGFILE%

   This renames the old log file with a timestamp.

5. Example: Logging Backup Script

   @ECHO OFF
   SET LOGFILE=backup.log
   
   CALL :Log "Backup started"
   
   XCOPY C:\Important D:\Backup /E /I >> %LOGFILE% 2>&1
   IF ERRORLEVEL 1 (
       CALL :Log "ERROR: Backup failed!"
   ) ELSE (
       CALL :Log "Backup completed successfully."
   )
   
   CALL :Log "Script finished."
   GOTO :EOF
   
   :Log
   ECHO [%DATE% %TIME%] %~1 >> %LOGFILE%
   EXIT /B

✅ Summary Table

Technique	Example	Purpose
Redirect stdout + stderr	CMD > log.txt 2>&1	Capture all output
Append logs	>> log.txt	Preserve previous logs
Add timestamps	[%DATE% %TIME%] in ECHO	Time tracking
Use logging subroutine	CALL :Log "Message"	Clean reusable logging
Log rotation	REN log.txt old_timestamp.log	Manage large logs
Separate logs	> output.log 2> error.log	Organized debugging