PowerShell's Top Ten Parameters (Switches)

PowerShell's Top Ten Parameters, or -Switches

Most of PowerShell's commands can be fine-tuned with -parameters, otherwise known as switches.  My aim of this page is to encourage you keep a notebook of such useful PowerShell parameters.  To begin with, let me explain the basics with an example; here is a command which searches just the top level container:
get-Childitem c: \windows

Now when you add the -recurse parameter, the command takes longer to execute, but it's well worth the time to drill down the directory tree, and find the file that you are seeking in a sub-directory:
get-Childitem c: \windows -recurse

Topics for PowerShell's Parameters

• Guy's Top Ten PowerShell -Parameters
• How to research more PowerShell Parameters or -Switches
• The Concept of an Optional, or an Assumed Parameter
• Pattern Matching Switches

Guy's Top Ten PowerShell -Parameters

1. -list with get-WmiObject (get-Eventlog -list)
2. -auto (Adjust the width with format-Table)
3. -MemberType (get-Member)
4. -recurse with get-ChildItem (Sub-directories)
5. -force with get-ChildItem (Lists hidden files)
6. -groupBy (Collate similar items)
7. -query (WMI Select statement)
8. -filter (get-Wmiobject "Win32_Process")
9. -com (new-Object)
10. -whatif (Test before you commit)

The technique is to add the parameter directly after the main command.  Remember to introduced your parameter or switch with a -minus sign, and not a backslash.  If you apply the terminology strictly, then the difference between a parameter and a switch is that a switch does not take a value, whereas a parameter can.

How to research more PowerShell Parameters or -Switches

If you play strategic games like chess, you may be familiar with the idea of once you have found a good move, then look for an even better tactic.  So it is with PowerShell, if you find a good command such as get-Eventlog system, look for parameter to refine the output, for example: get-Eventlog system -newest 20.

The key question is how did I know about the -newest parameter, as PowerShell calls this appendage?  The answer is I called for help. get-help get-Eventlog.  Or better still: get-help -Eventlog -full.  I recommend that you spend time studying the PARAMETERS section.

The Concept of an Optional, or an Assumed Parameter

If you digest every nuance of what get-help says, then you discover that each Parameter has properties, e.g.:
Required?  True or False
Position: 1 or 2 etc.

Both logic and practical experience show that if a parameter is not required, and it's in position 1, then you could safely omit it.  In other words the parameter is assumed.  Let us use get-Childitem and -path as an example:

get-Childitem -path c:\windows

get-Help get-Childitem

PARAMETERS
    -path
         Required?  False
         Position?   1

Thus get-Childitem - path c:\windows could be reduced to plain
get-Childitem c:\windows.   (or even: gci c:\windows)

Another example of an assumed parameter comes from get-Eventlog.  This command will not work unless you help PowerShell by supplying the name of the log.  The parameter is -LogFile.  For example get-Eventlog -LogFile system.  However, PowerShell understands that the first word after eventlog is the name the log, and thus we can omit the -Logfile parameter.  PowerShell assumes that the only possible parameter in this position is -LogFile and the following command completes successfully: get-Eventlog system.

Second series of useful PowerShell -Switches

1. -path (Example of an optional or assumed parameter)
2. -filePath (Variation on -path, used with Out-file)
3. -replace (select-String)
4. -pattern  (select-String)
5. -descending (sort-Object)
6. -value (add-Content)
7. -newest (get-Eventlog)
8. -last (Win32_Process pageFaults -last 5)
9. -computerName (Useful scripts requiring loops)
10. -computer (works equally well in most scripts)

Pattern Matching Switches

PowerShell also has a family of comparison or pattern matching switches.  You may see these conditional operators such as -match and -like in 'Where' clauses, for example:

get-wmiobject -list | where {$_.name -match "Win32"}

This family of switches has several names, conditional operators and pattern matching switches, let me introduce the family:

1. -match
2. -like
3. -contains

Sometimes logic dictates that their negative cousins produce tighter code, for example: -notmatch

Although we are straying further from my original idea of switches to modify a command, I should mention the logical operators as they too are introduced by a -dash.

1. -eq  (Beware in PowerShell you cannot substitute an equals sign for -eq)
2. -ne (Not equal, incidentally -neq will not work)
3. -and
4. -or

There are also bitwise variants -bor -band.  This is not an exhaustive list, there are exotic operators such as an exclusive or called -xor.

Summary of PowerShell's Parameters

Understanding PowerShell's parameters will improve your scripts.  Firstly, you get extra capabilities, for example -recurse, secondly you greater precision, for example -MemberType.  In conclusion, never miss a chance to research a Parameter or a Switch, if you find a really good example, email me and I will add it to Guy's top 10 Switches.

See Also PowerShell Tutorials:

• PowerShell Home  • Com  • Shell Application  • Active Directory  • QAD Snap-in  • Get-Member

Please write in if you see errors of any kind.  Please report any factual mistakes, grammatical errors or broken links, I will be happy to not only to correct the fault, but also to give you credit.

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