Skip to main content

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%

Labels:

Popular posts from this blog

How to do Git Rebase in Eclipse

This is an abbreviated version of a fuller post about Git Rebase in Eclipse. See the longer one here : One side-effect of merging Git branches is that it leaves a Merge commit. This can create a history view something like: The clutter of parallel lines shows the life spans of those local branches, and extra commits (nine in the above screen-shot, marked by the green arrows icon). Check out this extreme-case history:  http://agentdero.cachefly.net/unethicalblogger.com/images/branch_madness.jpeg Merge Commits show all the gory details of how the code base evolved. For some teams, that’s what they want or need, all the time. Others may find it unnecessarily long and cluttered. They prefer the history to tell the bigger story, and not dwell on tiny details like every trivial Merge-commit. Git Rebase offers us 2 benefits over Git Merge: First, Rebase allows us to clean up a set of local commits before pushing them to the shared, central repository. For this
Read more

Java 8: Rewrite For-loops using Stream API

Java 8 Tip: Anytime you write a Java For-loop, ask yourself if you can rewrite it with the Streams API. Now that I have moved to Java 8 in my work and home development, whenever I want to use a For-loop, I write it and then see if I can rewrite it using the Stream API. For example: I have an object called myThing, some Collection-like data structure which contains an arbitrary number of Fields. Something has happened, and I want to set all of the fields to some common state, in my case "Hidden"
Read more

Git Reset in Eclipse

Using Git and the Eclipse IDE, you have a series of commits in your branch history, but need to back up to an earlier version. The Git Reset feature is a powerful tool with just a whiff of danger, and is accessible with just a couple clicks in Eclipse. In Eclipse, switch to the History view. In my example it shows a series of 3 changes, 3 separate committed versions of the Person file. After commit 6d5ef3e, the HEAD (shown), Index, and Working Directory all have the same version, Person 3.0.
Read more

Code Coverage in C#.NET Unit Tests - Setting up OpenCover

The purpose of this post is to be a brain-dump for how we set up and used OpenCover and ReportGenerator command-line tools for code coverage analysis and reporting in our projects. The documentation made some assumptions that took some digging to fully understand, so to save my (and maybe others') time and effort in the future, here are my notes. Our project, which I will call CEP for short, includes a handful of sub-projects within the same solution. They are a mix of Web APIs, ASP MVC applications and Class libraries. For Unit Tests, we chose to write them using the MSTest framework, along with the Moq mocking framework. As the various sub-projects evolved, we needed to know more about the coverage of our automated tests. What classes, methods and instructions had tests exercising them, and what ones did not? Code Coverage tools are conveniently built-in for Visual Studio 2017 Enterprise Edition, but not for our Professional Edition installations. Much less for any Commun
Read more

Scala Collections: A Group of groupBy() Examples

Scala provides a rich Collections API. Let's look at the useful groupBy() function. What does groupBy() do? It takes a collection, assesses each item in that collection against a discriminator function, and returns a Map data structure. Each key in the returned map is a distinct result of the discriminator function, and the key's corresponding value is another collection which contains all elements of the original one that evaluate the same way against the discriminator function. So, for example, here is a collection of Strings: val sports = Seq ("baseball", "ice hockey", "football", "basketball", "110m hurdles", "field hockey") Running it through the Scala interpreter produces this output showing our value's definition: sports: Seq[String] = List(baseball, ice hockey, football, basketball, 110m hurdles, field hockey) We can group those sports names by, say, their first letter. To do so, we need a disc
Read more