{"id":10591,"date":"2006-04-25T12:18:15","date_gmt":"2006-04-25T12:18:15","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/powershell\/2006\/04\/25\/invoking-scriptblocks-from-c\/"},"modified":"2019-02-18T13:24:55","modified_gmt":"2019-02-18T20:24:55","slug":"invoking-scriptblocks-from-c","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/powershell\/invoking-scriptblocks-from-c\/","title":{"rendered":"Invoking Scriptblocks from C#"},"content":{"rendered":"

Last time somebody asked for an example of a C# method that took a scriptblock.  <\/span>First of all, there\u2019s one very important thing you have to know about scriptblocks as they are currently implemented.  <\/span>They can\u2019t be invoked outside of a runspace.  <\/span>Any attempt to do so will result in an exception.  <\/span>Some of you may already have found this out when using scriptblocks as delegates.  <\/span>Here\u2019s a quick demonstration of what happens when you try it:<\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

        <\/span>static<\/span><\/font> void<\/span><\/font> Main(string<\/span><\/font>[] args)<\/span><\/font><\/p>\n

        <\/span>{<\/span><\/font><\/p>\n

            <\/span>try<\/span><\/font><\/span><\/font><\/p>\n

            <\/span>{<\/span><\/font><\/p>\n

                <\/span>RunspaceInvoke<\/span><\/font> invoke = new<\/span><\/font> RunspaceInvoke<\/span><\/font>();<\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

                <\/span>ScriptBlock<\/span><\/font> scriptblock = invoke.Invoke(<\/span><\/font><\/p>\n

                  “{ return ‘foo’; }”<\/span><\/font>)[0].BaseObject as<\/span><\/font> ScriptBlock<\/span><\/font>;<\/span><\/font><\/p>\n

                <\/span>scriptblock.Invoke();<\/span><\/font><\/p>\n

            <\/span>}<\/span><\/font><\/p>\n

            <\/span>catch<\/span><\/font> (Exception<\/span><\/font> e)<\/span><\/font><\/p>\n

            <\/span>{<\/span><\/font><\/p>\n

     <\/span>           <\/span>Console<\/span><\/font>.WriteLine(e);<\/span><\/font><\/p>\n

            <\/span>}<\/span><\/font><\/p>\n

            <\/span>finally<\/span><\/font><\/span><\/font><\/p>\n

            <\/span>{<\/span><\/font><\/p>\n

                <\/span>Console<\/span><\/font>.WriteLine(“Press any key to exit…”<\/span><\/font>);<\/span><\/font><\/p>\n

                <\/span>Console<\/span><\/font>.ReadKey();<\/span><\/font><\/p>\n

            <\/span>}<\/span><\/font><\/p>\n

        <\/span>}<\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

Which results in the following exception message\u2026<\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

System.Management.Automation.MshInvalidOperationException: A script block delega<\/font><\/font><\/span><\/font><\/p>\n

te was invoked from the wrong thread. It is permitted to pass a script block as<\/font><\/font><\/span><\/font><\/p>\n

a delegate, but the delegate may only be invoked from a runspace thread. The scr<\/font><\/font><\/span><\/font><\/p>\n

ipt block you attempted to invoke was: return ‘foo’;<\/font><\/font><\/span><\/font><\/p>\n

   <\/span>at System.Management.Automation.ScriptBlock.UpdateUsingInfoFromTLS()<\/font><\/font><\/span><\/font><\/p>\n

   <\/span>at System.Management.Automation.ScriptBlock.InvokeWithPipe(Boolean UseLocalSc<\/font><\/font><\/span><\/font><\/p>\n

ope, Boolean writeErrors, Object dollarUnder, Object input, Object scriptThis, P<\/font><\/font><\/span><\/font><\/p>\n

ipe outputPipe, ArrayList& resultList, Object[] args)<\/font><\/font><\/span><\/font><\/p>\n

   <\/span>at System.Management.Automation.ScriptBlock.Invoke(Object dollarUnder, Object<\/font><\/font><\/span><\/font><\/p>\n

 <\/span>input, Object[] args)<\/font><\/font><\/span><\/font><\/p>\n

   <\/span>at System.Management.Automation.ScriptBlock.Invoke(Object[] args)<\/font><\/font><\/span><\/font><\/p>\n

   <\/span>at Test.Program.Main(String[] args) in c:\\Temp\\ConsoleApplication15\\Program.c<\/font><\/font><\/span><\/font><\/p>\n

s:line 23<\/font><\/font><\/span><\/font><\/p>\n

Press any key to exit…<\/font><\/font><\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

So\u2026 creating scriptblocks and taking them out of the runspace for invocation is out of the question for now\u2026  <\/span>You could of course send the scriptblock back into a runspace and invoke it there.  <\/span>Lets try that, and just for fun we\u2019ll invoke the scriptblock in a different runspace than the one it was created in:<\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

                <\/span>RunspaceInvoke<\/span><\/font> invoke = new<\/span><\/font> RunspaceInvoke<\/span><\/font>();<\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

                <\/span>ScriptBlock<\/span><\/font> scriptblock = invoke.Invoke(<\/span><\/font><\/p>\n

                  “{ return ‘foo’; }”<\/span><\/font>)[0].BaseObject as<\/span><\/font> ScriptBlock<\/span><\/font>;<\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

                <\/span>\/\/A second runspace.<\/span><\/font><\/span><\/font><\/p>\n

                <\/span>RunspaceInvoke<\/span><\/font> mySecondInvoke = new<\/span><\/font> RunspaceInvoke<\/span><\/font>();<\/span><\/font><\/p>\n

                <\/span>Collection<\/span><\/font><MshObject<\/span><\/font>> results = mySecondInvoke.Invoke<\/span><\/font><\/p>\n

                  (“$script = $input | write-object; & $script”<\/span><\/font>,<\/span><\/font><\/p>\n

<\/span><\/font>                  new<\/span><\/font> object<\/span><\/font>[] { scriptblock });<\/span><\/font><\/p>\n

                <\/span>string<\/span><\/font> resultStr = results[0].BaseObject.ToString();<\/span><\/font><\/p>\n

                <\/span>Console<\/span><\/font>.WriteLine(resultStr);<\/span><\/font><\/span><\/font><\/p>\n

Which results in:<\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

foo<\/font><\/span><\/font><\/p>\n

Press any key to exit…<\/font><\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

So grabbing a scriptblock from one runspace and sending it across to another runspace works.  <\/span>When doing this you should always keep in mind that these are different runspaces with different SessionState so variables, providers and cmdlets that exist in one runspace might not exist in the other.  <\/span>It all depends, of course, on how you created the runspace and what you\u2019ve run after it was created.  <\/span>Anyway, getting back to the original subject, what we really wanted was an example of a C# method that takes a scriptblock.  <\/span>Well\u2026 while you can\u2019t invoke a scriptblock outside of the runspace thread, you CAN call C# methods from Monad.  <\/span>And if you call a C# method from Monad, it gets invoked on the runspace thread.  <\/span>So\u2026. to try this out, the first thing we need is a method that takes a ScriptBlock.<\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

        <\/span>public<\/span><\/font> static<\/span><\/font> string<\/span><\/font> MyTestMethod(ScriptBlock<\/span><\/font> scriptBlock)<\/span><\/font><\/p>\n

        <\/span>{<\/span><\/font><\/p>\n

            <\/span>return<\/span><\/font> scriptBlock.Invoke(“foobar”<\/span><\/font>)[0].ToString();<\/span><\/font><\/p>\n

        <\/span>}<\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

Now\u2026 all we need to do is invoke this static method and get the results.  <\/span>A slight modification of our earlier program will do the trick.<\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

        <\/span>static<\/span><\/font> void<\/span><\/font> Main(string<\/span><\/font>[] args)<\/span><\/font><\/p>\n

        <\/span>{<\/span><\/font><\/p>\n

            <\/span>try<\/span><\/font><\/span><\/font><\/p>\n

            <\/span>{<\/span><\/font><\/p>\n

                <\/span>RunspaceInvoke<\/span><\/font> ri = new<\/span><\/font> RunspaceInvoke<\/span><\/font>();<\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

                <\/span>\/\/ Create a scriptblock and pass it to our <\/span><\/font><\/span><\/font><\/p>\n

                \/\/ static method.<\/span><\/font><\/span><\/font><\/p>\n

                <\/span>string<\/span><\/font> script = <\/span><\/font><\/p>\n

                    <\/span>“$script = { return $args; }              <\/span>\\r\\n”<\/span><\/font> +<\/span><\/font><\/p>\n

                    <\/span>“[Test.Program]::MyTestMethod($script);   <\/span>\\r\\n”<\/span><\/font>;<\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

                <\/span>string<\/span><\/font> scriptBlockResult = ri.Invoke(script)<\/span><\/font><\/p>\n

                     [0].ToString();<\/span><\/font><\/p>\n

                <\/span>Console<\/span><\/font>.WriteLine(scriptBlockResult);<\/span><\/font><\/p>\n

            <\/span>}<\/span><\/font><\/p>\n

            <\/span>finally<\/span><\/font><\/span><\/font><\/p>\n

            <\/span>{<\/span><\/font><\/p>\n

                <\/span>Console<\/span><\/font>.WriteLine(“Press any key to exit…”<\/span><\/font>);<\/span><\/font><\/p>\n

                <\/span>Console<\/span><\/font>.ReadKey();<\/span><\/font><\/p>\n

  <\/span>          <\/span>}<\/span><\/font><\/p>\n

        <\/span>}<\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

The script we are running is fairly simple.  <\/span>First it creates a scriptblock and assigns it to a variable.  <\/span>Then it calls the static method MyTestMethod on class Test.Program, passing it the scriptblock as an argument.  <\/span>If you compile and run this you\u2019ll get the following output:<\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

foobar<\/font><\/span><\/font><\/p>\n

Press any key to exit…<\/font><\/span><\/font><\/p>\n

 <\/span><\/font><\/p>\n

– Marcel<\/span><\/font><\/p>\n

[Edit: Monad has now been renamed to Windows PowerShell. This script or discussion may require slight adjustments before it applies directly to newer builds.<\/i>]<\/p>\n","protected":false},"excerpt":{"rendered":"

Last time somebody asked for an example of a C# method that took a scriptblock.  First of all, there\u2019s one very important thing you have to know about scriptblocks as they are currently implemented.  They can\u2019t be invoked outside of a runspace.  Any attempt to do so will result in an exception.  Some of you […]<\/p>\n","protected":false},"author":600,"featured_media":13641,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-10591","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-powershell"],"acf":[],"blog_post_summary":"

Last time somebody asked for an example of a C# method that took a scriptblock.  First of all, there\u2019s one very important thing you have to know about scriptblocks as they are currently implemented.  They can\u2019t be invoked outside of a runspace.  Any attempt to do so will result in an exception.  Some of you […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/posts\/10591","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/users\/600"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/comments?post=10591"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/posts\/10591\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/media\/13641"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/media?parent=10591"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/categories?post=10591"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/tags?post=10591"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}