Moritz Schepp

First steps with Windows Powershell

After a training session with a group of colleagues, I wanted to put this together for future reference and for getting started the next time I actually want to automate something on a windows host. As such, this is not a full tutorial but rather a loose collection of facts and Q&A.

For a good listing of the various versions and platforms, have a look at the wikipedia article.

Facts

  • $PSVersionTable holds the Version of the currently running PowerShell instance
  • PowerShell lets you chain so called cmdlets which originate from the core modules or from modules included in software packages like Microsoft Exchange Server
  • cmdlets mostly adhere to a syntax describing a CRUD pattern: New-..., Get-..., Set-..., Remove-...
  • PowerShell comes with the ISE (integrated scripting environment) which is an IDE to compose, manage and run scripts
  • the file name extension for scripts is .ps1
  • GetHelp <cmdlet> shows the help entry for that cmdlet (it might be necessary to run Update-Helpto generate the help content on that host)
  • piping output from one command to the input of another is done with the | symbol. Be aware that unlike on UNIX-like systems, this passes along actual objects and not simply lines of text.
  • filtering the output of a command by text can still be done by with findstr (the PowerShell equivalent for grep)
  • pipe output to More so that output can be controlled by keyboard cursors or the space key
  • Get-Member retrieves a list of all member (attributes and methods) of a given object
  • running scripts might be disabled via execution policy. You may activate it permanently on that host with Set-Execution-Policy unrestricted
  • capitalization doesn’t matter: Get-Member is equivalent to get-member
  • Get-Command lists installed cmdlets

Investigate

  • how are encodings dealt with? Ineresting: http://superuser.com/questions/327492/default-powershell-to-emitting-utf-8-instead-of-utf-16
  • remote execution
  • does every cmdlet always output lists of objects even if there is only one object to be returned (kind of like bash commands always return a list of lines, potentially just one)?
  • how is white space treated? how about newlines?
  • how to organize scripts? how to load, eval or require scripts?
  • do scripts halt when an error is encountered (bash scripts only do that with the -e switch)?
  • variable scope?
  • is there a canonical way for dependency management (like bundler for ruby or compozer for php)?
  • what data types are there, or is there just <list-of-objects>

Examples

List available logs

Get-EventLog -list

How to grep the logs for (e.g.) “Update”:

Get-EventLog System | findstr Update