Learning PowerShell with Kiran …… day two

Getting help

Powershell is an excellent tool in that, all the required documentation is built into the shell itself. You do not have reference and developer documentation etc., as you do a lot with vbscript.

help <cmdlet or alias>

will give you the needed help required with the syntax. If you need a more detailed help explaining all the options or examples, then just use the switch –detailed or –full

help <cmdlet or alias> –full

help <cmdlet or alias> –detailed

eg: help <Get-ChildItem> –full

Help feature also supports wildcards. ie., if you are looking for a cmdlet to stop a process, then you could simply “help *process* ” as shown below:

from the above, it is relatively easy to figure out that, “Stop-Process” is the cmdlet, you can use to stop a process. Quite powerful isn’t it.

Working with Aliases

Using Aliases instead of cmdlets is convenient. ‘causing typing long cmdlet names is not only cumbersome, its also prone to mistakes, and you easily get frustrated if you use them regularly. So, to keep your sanity, PowerShell provides the alias feature. If you are from the *nix world, then you already know what alias is. Aliases can be used to call the cmdlets with shorter names for convenience instead of using their full cmdlet names.

dir, ls, copy, cd are system assigned aliases for Get-ChildItem, Copy-Item, and Set-Location. PS has many more aliases and to list them, you can use the command…..wait, how can we find out what command do we use…let’s try using help here.

Looking at the output, I am tempted to try “Get-Alias”

That’s it. That how we explore the power of PS.

If I want to know the available aliases for Get-ChildItem, then I have to look at help to see all the option and switches provided by the cmdlet.

PS> help Get-Alias –full

shows this interesting example

 

Exactly what we need. Now let’s try that.

Understanding the above command in its simplest form(don’t get hung up on the functions, neither will I), its piping the output of the get-alias command and filtering out only the data where “Get-ChildItem” exists in Column “Definition”. Awesome…. Now this means, that PS also supports piping.

You can create your own aliases using the “New-Alias” command option. We have seen this in the second screenshot (help *alias*). The command syntax can be obtained by looking up help on New-Alias.

In its simplest form, you can use the command as below:

PS> New-Alias –name d –value GetChildItem

or

You could also specify it as below:

PS> New-Alias d GetChildItem

‘cause PS does not require you to specify the positional parameter name, if its specified in the right order. ie., in this case the first parameter that New-Alias takes is “-name” and the second parameter that it takes is “-value”. As long as we have the right values in the right order, PS will interpret them properly.

To check if the command worked, lets retry the get-alias command using where_object filtering:

Yes, “d” does show up as an alias. Lets run the command:

Delete an Alias

I’m not sure if you remember the screenshot from Day One, which reveals that Alias is also loaded as a PSDrive. which means I can also get a list of aliases by issuing a “Get-ChildItem” or “dir” against it as shown below:

which also will probably allow me to use “Remove-Item” to remove any alias that I do not need. Let’s try it.

Yup. That worked.

Finding the required cmdlet

In the beginning of this post, we used “help” command to search for required cmdlets. This is only looking at the documented help topics to get you the required information. If there are cmdlets that are not documented, then you would not find them. To find any cmdlet, you should ideally use the “Get-Command”.

Just issuing “Get-Command” by itself will list all the available cmdlets in the shell.

To understand the syntax of Get-Command let’s run “help Get-Command”

Notice the “-verb” and “-noun” parameters. This is what makes Get-Command powerful and useful in searching cmdlets. Remember on Day One we talked about how PS uses verb-singularnoun convention to name all its cmdlets. The power of doing so is revealed now.

eg: you want to look for a process on your machine and kill it, and we obviously do not know the cmdlet to do that. So lets use Get-Command to achieve this. Since we want to look at process let’s ask for all command lets that match the noun process.

So, we have two choices with processes. “Get-Process” and “Stop-Process”. See how powerful and easy it makes finding cmdlets. In addition to this the parameters support wildcards too as shown below

PS Snap-ins

Cmdlets themselves are packaged in snap-ins. Each snap-in adds additional functionality and cmdlets to the shell. Very much like mmc snap-ins. The cmdlets used to manage snap-ins can be found by using the Get-Command described above.

 

We can make an educated guess, that Add-PSSnapin is to add new Snap-ins and Remove-PSSnapin is to remove Snap-ins from the shell. Get-PSSnapin is probably used to get details about a Snap-in. Let’s check.

As evident, running Get-PSSnapin, when run by itself, lists all the available snap-ins on this computer. We also notice that it can used to search for a particular snap-in using the –name parameter, which also accepts wildcards. In this case, we tried to look for any snap-in that has the word “Utility” in it.

To see available cmdlets in a snap-in, we may have to look at Get-Command cmdlet’s syntax more closely.

oh, wait, yes, Get-Command takes –pSSnapIn as an argument. Wonderful. Let’s try that:

Learning PowerShell With Me ..

Day one

What is Powershell ?

Install Powershell

You have to download and install Powershell for windows XP and Vista, but its included in Windows 2008 and windows 7 by default. You just have to enable the feature in Windows 2008.

Lets Begin

start the powershell prompt.

A powershell prompt looks very much like a windows command prompt and almost all of the windows commands work well in the powershell command window with a few exceptions. For all of you unix lovers and that includes me, most of the unix commands work well inside powershell too.

Lets start with Dir

Dir command without any switches works exactly the same way it would in a command prompt.

Dir c:

but wait Dir c:\program files will not work without the quotes surrounding it, 'cause powershell treats “space” as the delimiter between command and its parameters. So, you should surrounding your path with quotes, to enable powershell to see the whole path properly

dir “c:\program files”

Powershell comes with a ton of help, that is readily accessible by using help <commandname>. The help context also supports wildcards.

Help <commandname> -full

will give you a very detailed explanation of the command with examples too.

Type in help dir

did you notice that the actual command is called Get-ChildItem. And it provides a bunch of parameter options like -recurse etc., This leads me to believe that “dir” or “ls” are probably aliases for the command Get-ChildItem. I'll probably find out as i go. Personally, i would think its better to stick with the actual cmdlets (yes, these commands are implemented as scripts called cmdlets), than with the aliases, 'cause it will help you get acquainted with the cmdlets and understand the code better as we move on, atleast for the duration of learning powershell. Once you get into actual implementation in real life, its up to. As for me, I'm going to stick with the cmdlets.

So to list a directory:

Get-ChildItem c:\perflogs

or

Get-ChildItem “c:\program files”

to recursively display a folder content

Get-ChildItem -recurse “c:\program files”

gives a long listing, use Ctrl +C, looks like that works in powershell as “Break” too.

PowerShell has the unique ability to navigate an hierarchical structure just like a file system viz., registry or active directory or storage systems. This is awesome, so you could navigate registry like below:

Get-ChildItem HKCU:

will list out the contents of HKEY_CURRENT_USER

Guess what the below command does:

Get-ChildItem HKCU: -recurse

you could also change your current location into the registry viz., below:

cd HKLM:\Software

or Set-Location HKLM:\Software
(yes, “cd” is the alias for cmdlet “Set-Location”, as i said, I'm going to stick with cmdlet names instead of aliases)

Same thing can be applied to Environment Variables also. Eg:

Set-Location ENV:

Get-ChildItem ENV:

Get-ChildItem ENV:\systemroot

Copy Items

“Copy” is another most used dos command. And the it works the same in powershell too. “Copy” is an alias for cmdlet “Copy-Item”.

Help Copy

or

Help Copy-Item

will reveal all the switches available for the cmdlet. Most commonly use switch would probably be “-recurse”

Delete Items

RD, Del or rm will work exactly as expected, but the underlying cmdlet for all this is “Remove-Item”

you could use rd or del or rm to achieve the same result eg:

rd c:\temp\test.txt

or

del c:\temp\test.txt

or

Remove-Item c:\temp\test.txt

you could also use the same “-recurse” switch to recursively delete folders.

Read contents of a file

Most of us are used to “TYPE” or “CAT” commands to achieve this. The same works in PowerShell too. Eg:

type c:\temp\test.txt

cat c:\temp\test.txt

or use the cmdlet directly

Get-Content c:\temp\test.txt

PowerShell Drives (PSDrives)

As we have seen, powershell lets you navigate registry, storage systems, environment variables etc., using simple navigation commands that we are used to. It can do that, 'cause it loads them as Psdrives or PowerShell Drives.

To see a list of all these PowerShell drives, which you can navigate, type in the below:

Get-PSdrive

This will show you all the drives that PowerShell has loaded. The power of navigating through certificate stores, Environment Variables and functions is amazing.

Did you notice that PS (PowerShell) has loaded “alias” as a drive. So lets see all the aliases that PS has built-in by listing the contents of the drive.

Get-ChildItem alias:

WOW!, that's a nice list of aliases that can be used. It would be handy to have a printed list (cheatsheet)
of these aliases that you can pinup at your desk. I'll make one up.

Cmdlet Naming syntax

The beauty of the long names is that, they have a consistent naming syntax. Each command has a verb-Singularnoun, syntax. ie., the cmdlet starts with a verb viz., get, remove etc., and ends with the singularnoun, ie., ChildItem, content, Psdrive etc., Stress on the word Singular, 'cause none of the commands actually end in plural, there is no Get-ChildItems or Get-Contents. Cmdlets nouns always are Singular.

Eg: issue the command below to see a list of all cmdlets available to powershell

Get-Command

Notice how all the cmdlets start with a verb, and end with a singular noun. None of them have a plural form.

The reason, this is done, is that, it is easier to search of a particular cmdlet, when needed.

Hope you have already started to ride with me and will continue .......