I took a session on Monad at the Bangalore .NET User Group meeting yesterday. Here is a brief write-up about the session for those of you who missed the session. People starting off on Monad may be interested in reading this.
Introduction
Unlike conventional shells that work on text streams and expect the end user to be an expert in text parsing, MSH introduces the idea of using structured object pipelines where objects instead of text flow between commands.
At the msh prompt, if we type
MSH C:/ > dir
we see a list of files [the same way the dos dir worked]. We see the same output for ls.
In Monad commands are called cmdlet [Commandlets]. Each cmdlet is a combination of a verb-noun pair. For example the cmdlet get-children or get/children gets all the children [files and directories when invoked in a FS]. dir and ls are aliases of get-children. By default the verb ‘get’ is assumed for a command given without a verb. So typing children gives the result of get-children and command gives the result of get-command. Alias is an exception. Typing alias gives the result of set-alias and typing aliases give the result of get-alias.
To see all the commands type command. To see all the aliases type aliases.
Some example Commands
MSH C:/> get-process
By using reflection, any object can list the methods and properties that it supports. To get a list of methods supported by a get-process object [which is a System.Diagnostics.Process object] try the command below.
MSH C:/> get-process | get-member -methods
MSH C:/> $a = get-process
MSH C:/> $a[0]
MSH C:/> $a[0].ToString()
Here $a is an array of Process Objects. We can invoke any function or property from the process class on object $a[0] and see the results like the ToString() example above.
MSH C:/> get-process | get-member -property
MSH C:/> $a[0].handlecount
MSH C:/> gps
MSH C:/> gps | tail
MSH C:/> gps | sort id | tail
MSH C:/> gps | where “processname –like cmd*”
MSH C:/> gps | reduce-expression {$_.handlecount -ge 500}
get-process or gps returns an array of objects. Reduce-expression works like a lambda in functional programming languages [similar to anonymous method]
For example in scheme (lambda((a b)(+ a b))) acts as a block of code.
In Monad the block of code after reduce-expression in braces is the script that will be carried for each pipeline object. $_ is set to the current pipeline object. So for each object in the object array returned by gps, $_ is filled with an object (the current pipeline object) for which the block of code is executed.
MSH C:/> gps | sort handlecount | tail | out-excel
MSH C:/> get-process | out-chart processname,handlecount -Title "Processes" -Filename Processes.html
MSH C:/> gps | sort handlecount | tail | out-grid processname,handlecount
MSH C:/> get-command out-*
MSH C:/> foreach ($p in $a | where "handlecount -ge 500" | sort handlecount) { "{0,-15} has {1,6} handles" % $p.processname,$p.handlecount }
Notice the .NET style for formatting strings above.
MSH C:/> function n{notepad}
MSH C:/> n
MSH C:/> n;n;n
MSH C:/> gps [a-c]*,[t-z]* -exclude *[p-t] | stop-process –whatif
MSH C:/> gps | where “processname –like notepad*” | stop-ps1 –confirm
For invalid process ids, an error message is displaying when trying to stop them.
MSH C:/> stop-process 123,345,100000,200000,300000
MSH C:/> stop-process 123,345,100000,200000,300000 -errorpolicy notifystop
MSH C:/> stop-process 100000,200000,300000 -errorpolicy inquire
[Error stop-process]: (No process found for given ID : : 100000) 100000"
[Error stop-process]: (No process found for given ID : : 100000) 100000"
Continue :[y/yes/ n/no t/yestoall l/notoall s/suspend] s
MSH C:/> exit
[Error stop-process]: (No process found for given ID : : 100000) 100000"
Continue :
[y/yes/ n/no t/yestoall l/notoall s/suspend] l
Stopped (Cmdlet:stop-process): User requested stop
MSH C:/>
Cmdlet
Each cmdlet is a managed class and not a separate executable. A simple cmdlet code is given below.
using System;
using System.Diagnostics;
using System.Management.Automation;
namespace SampleCmdlet
{
#region GetPs1
[CmdletDeclaration("get", "ps1")]
public class GetPs1: Cmdlet
{
public override void ProcessRecord()
{
WriteObjects(Process.GetProcesses());
}
}
#endregion
}
The class that is to be exposed as a cmdlet is annotated with a CmdletDeclaration property specifying the verb and noun that is to be used to access this cmdlet. Also your class must inherit from the Cmdlet class and override atleast one of the three functions StartProcessing, ProcessRecord and EndProcessing.
A cmdlet that receives some input parameters and does exception-handling is given below
using System;
using System.Diagnostics;
using System.Management.Automation;
namespace SampleCmdlet
{
#region StopPs1
[CmdletDeclaration("stop", "ps1")]
public class StopPs1: Cmdlet
{
[ParsingParameterMapping(0)]
[ParsingAllowPipelineInput]
[ParsingMandatoryParameter]
[ParsingPromptString( "Input the id: " )]
public int [] Id;
public override void ProcessRecord()
{
Process p = null;
foreach ( int i in Id )
{ if (ShouldProcess(i.ToString()))
{
try
{
p = Process.GetProcessById(i);
p.Kill();
}
catch (System.ComponentModel.Win32Exception e)
{ WriteErrorObject("No adequate permissions",e); }
catch (System.ArgumentException e)
{ WriteErrorObject("No such process exists",e); }
}
}
}
}
#endregion
}
The code declares the input parameter, annotates it with attributes and assumes that the input values have been filled in. It doesn’t care if the input is coming form the pipeline, file, console or any other means. All the parsing and filling up the value is taken care by the shell. The same goes for output. The code calls WriteObject() function to do any output and the shell takes care of the formatting, displaying and routing of output as per the context.
The code above is for Monad, March 2004 build. Sample code for July, 2004 build is available at
http://msdn.microsoft.com/theshow/Episode043/Transcript.html
Cmdlet Providers
Cmdlet Providers provide the user with a basic set of cmdlets like pushd, move, copy, cd, dir etc that make the provider as navigable as a file store. Two standard providers come with the msh installation, one for registry browsing and the other for active directory.
[ProviderDeclaration("REG", "Microsoft", "Windows", "6.0", "MSH", "Registry", "1.0", ProviderCapabilityFlags.None)]
public class RegistryProvider : NavigationCmdletBase
{
protected override void GetItem(string path)
{
RegistryKey key = GetRegkeyForPath(path, false);
if (key == null)
{ WriteErrorObject(path, new ArgumentException("does not exist"));
}
WriteObject(key);
}
....
}
For installing registry provider use:
MSH C:/> new-provider -Assembly "${MSHHOME}\System.Management.Automation.Core.dll" -Provider REG
Registry Example
To add a new item to the context menu of directories, some values need to be added to the registry. Here is an example that adds a “Launch MSH” option in the context menu of a directory such that on right clicking a directory and selecting “Launch MSH”, Monad is launched and a changedir [or cd] to the corresponding directory is done.
For this we create new items, “Launch msh” and “Command: in the registry using msh commands to give HKLM:/Software/Classes/Directory/Shell/Launch MSH/Command. Note: The escape character in MSH is ` => the back quote character.
MSH C:/> $val = format-string "`"{0}`" `"{1}`" `"{2}`" " "${MSHHOME}\msh.exe" "-command" "cd '%1' "
MSH C:/> $val
MSH C:/> new-item -path "HKLM:/SOFTWARE/Classes/Directory/shell" -name "Launch MSH"
MSH C:/> new-item -path "HKLM:/SOFTWARE/Classes/Directory/shell/Launch MSH" -name "Command"
MSH C:/> set-item -path "HKLM:/SOFTWARE/Classes/Directory/shell/Launch MSH/Command" –value $val
Now on right clicking any directory an option “Launch MSH” should appear. On selecting that option, MSH is launched with the current directory as the directory that was right clicked. Neat?
MSH C:/> Get-drive
MSH C:/> cd HKLM:/
MSH HKLM:/> dir
MSH HKLM:/> cd Software
Yeah, the registry provider lets you move through the registry just the way you move through a file system!
Download and Installation
Monad Beta Release 1.0
- Go to beta.microsoft.com
- Sign in with your passport id
- Enter Guest login as mshPDC
- Fill up the form with your details and submit
- After 24-36 hours you should be able to login to the system. Click the downloads link on left pane
- Click the Microsoft Command Shell link.
- Download .NET framework 2.0. Install this [22.16MB] [It does not interfere with your earlier .NET versions]
- Download msh – Microsoft Command Shell Preview [1.88 MB]
System requirements
Windows XP or Windows Server 2003.
[If you are on another windows version read 1 and 2]
Reference Material
http://msdn.microsoft.com/theshow/Episode043/default.asp
The best way to learn monad is to download the shell and read the documentation that comes with the shell. As of now, there are no technical resources about the shell except for the video by Jeffrey Snover – Architect, Monad and Jim Truher – Program Manager, Monad[link above]
Take a look at profile.msh file that is installed along with Monad in the user’s home directory.
There is a lot of code using aliases, environment variables, functions, commandlets etc – a good place to pick up some tips from.
Do write to me your feedback about Monad – good and bad.