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Windows .BAT Script to launch task, then loop until done

My last post described my discovery of the Windows Schtasks.exe utility to trigger via the command-line a scheduled task on a local or - more relevant to the challenges I was facing - on a remote server. I described its ability to query the state of the task, and to launch it.

Of course, since my whole purpose was to automate a tedious manual section of our build process, Schtasks.exe is helpful but hardly the end of the story.

To benefit from that new knowledge, I now need to create a Windows shell script that our Continuous-Integration tool Jenkins can launch. This post is almost a stream-of-consciousness blog as I play with this problem.

The requirements are that the script launch the remote scheduled task, poll its status until it is complete, and end with an appropriate result code. Some minimal logging of activity would also be nice.

To begin, I created a .BAT file and created a labelled section to trigger the remote task:
:LaunchBuild
REM  QUESTION: What if it is already running? Should we wait? Abnormal-end? Skip?
schtasks /run /s MyRemoteServer /tn MyBuildTask


The REMark line raises a question that I will need to think about later. The remote scheduled task takes about 10 minutes to run (the manual steps took 20-30 minutes, so that's a vast improvement!). It might already be running. If it is, we should wait until it finishes. The Task Scheduler itself probably provides some assistance with this, so I make a note to look into this further, and return to the problem at hand.

I learned last time that I can query the state of the scheduled task with:
schtasks /v /query /s MyRemoteServer /tn MyBuildTask /FO LIST

But now I need to process the results and determine if the task has finished successfully, is still running, or is in some other state. By adding something like the following, I can parse the formatted output from the query:

FOR /F "tokens=1,2* delims=:" %%a in ('schtasks /v /query /s MyRemoteServer /tn MyBuildTask /FO LIST') DO (
if %%a==Status SET statusStr=%%b
if %%a==Last^ Result SET resultStr=%%b
)

Full confession: it took me a while to realize that I needed to escape the space in the comparison string. I was getting no value in the resultStr variable with "Last Result" with either single quotes, double quotes, or no quotes. But preceding it with the caret ^ character tells the IF comparison to treat the space as part of the string.

There is another step needed. The LIST formatted output has lots of spaces coming before the actual value, something like "              Running". We need to trim those spaces. I used this approach:
for /f "tokens=* delims= " %%a in ("%statusStr%") do set statusStr=%%a
for /f "tokens=* delims= " %%a in ("%resultStr%") do set resultStr=%%a

At last, I branched to a specific label-marked section of the script based on the status of the latest query:
IF %statusStr%==Ready GOTO:TaskReady
IF %statusStr%==Running GOTO:QueryStatus

So now I have a Windows .bat script that launches the remote scheduled task and monitors it so long as the status is Running. Once it switches to Ready, it breaks out of its loop. Now, it turns out that the Task Scheduler does not propagate error codes in quite the way I expected, so I have a little more work to do to get Jenkins to show an accurate status when the remote task fails.

But for now, with some light logging thrown in for sanity's sake, the final script looks more or less like the following. Again, I am not a SysAdmin and do not do a whole lot of work with .BAT files, but I am the lead for setting up Jenkins so it's me or no one.
REM @echo off
REM **************************************************
REM  This script launches the build task and queries the status while the task is still running.
REM **************************************************

:Begin
SETLOCAL
SET output=MyBuildStepLog.txt

REM **************************************************
REM  LaunchBuild
REM  Run the Scheduled Task on the remote server.
REM **************************************************
:LaunchBuild
REM QUESTION: What if it is already running? Should we wait? Abnormal-end? Skip?
CALL:Println "Launching the Build task on MyRemoteServer at %Time%"
schtasks /run /s MyRemoteServer /tn MyTask


REM **************************************************
REM  QueryStatus
REM  Query the current status of the Scheduled Task on the remote server.
REM   Scan the formatted output for the Status and the Last Result values.
REM     Since those values are padded with leading spaces, trim them.
REM  Branch either forward when status is Ready, or repeat the loop when Status is Running.
REM **************************************************
:QueryStatus
CALL:Println "Querying the status of the Build task at %Time%"
FOR /F "tokens=1,2* delims=:" %%a in ('schtasks /v /query /s MyRemoteServer /tn MyTask /FO LIST') DO (
if %%a==Status SET statusStr=%%b
if %%a==Last^ Result SET resultStr=%%b
)

for /f "tokens=* delims= " %%a in ("%statusStr%") do set statusStr=%%a
for /f "tokens=* delims= " %%a in ("%resultStr%") do set resultStr=%%a

CALL:Println "  Query result: at %Time% the status is: %statusStr% and the Last Result is: %resultStr%"
CALL:PrintEmptyln

IF %statusStr%==Ready GOTO:TaskReady
IF %statusStr%==Running GOTO:QueryStatus
GOTO:END

REM **************************************************
REM  TaskReady
REM **************************************************
:TaskReady
CALL:Println "The Build task is no longer running, status is Ready."
CALL:Println "The Build's Last Result is %resultStr%."
SET ErrorLevel=%resultStr%
GOTO:END


REM **************************************************
REM  Println
REM **************************************************
:Println %1
@echo %~1
@echo %~1 >> %output%
GOTO:EOF


REM **************************************************
REM  PrintEmptyln
REM **************************************************
:PrintEmptyln 
@echo.
@echo. >> %output%
GOTO:EOF


REM **************************************************
REM  End
REM **************************************************
:End
IF NOT %ErrorLevel%==0 CALL:PrintEmptyln
IF NOT %ErrorLevel%==0 CALL:Println "Error Number: %ErrorLevel%"
EXIT /B %ErrorLevel%

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