PowerShell, performance and regular expressions

Yesterday evening, I started to read Windows PowerShell in Action and did confirm what I had already read here and there: it’s a good book!

 So this morning, I was playing around and trying some of the stuff I had read:

> Get-Process | Get-Member

   TypeName: System.Diagnostics.Process

Name MemberType Definition

---- ---------- ----------

Handles AliasProperty Handles = Handlecount

Name AliasProperty Name = ProcessName

NPM AliasProperty NPM = NonpagedSystemMemorySize

PM AliasProperty PM = PagedMemorySize

VM AliasProperty VM = VirtualMemorySize

WS AliasProperty WS = WorkingSet

add_Disposed Method System.Void add_Disposed(EventHandler value)

add_ErrorDataReceived Method System.Void add_ErrorDataReceived(DataReceivedEventHandler value)

add_Exited Method System.Void add_Exited(EventHandler value)

add_OutputDataReceived Method System.Void add_OutputDataReceived(DataReceivedEventHandler value)

BeginErrorReadLine Method System.Void BeginErrorReadLine()

BeginOutputReadLine Method System.Void BeginOutputReadLine()

CancelErrorRead Method System.Void CancelErrorRead()

CancelOutputRead Method System.Void CancelOutputRead()

Close Method System.Void Close()

CloseMainWindow Method System.Boolean CloseMainWindow()

CreateObjRef Method System.Runtime.Remoting.ObjRef CreateObjRef(Type requestedType)

Dispose Method System.Void Dispose()

Equals Method System.Boolean Equals(Object obj)

GetHashCode Method System.Int32 GetHashCode()

GetLifetimeService Method System.Object GetLifetimeService()

GetType Method System.Type GetType()

get_BasePriority Method System.Int32 get_BasePriority()

…

I did not want to see those [get|set|add|remove]_ … methods! So I try something quick:

Get-Process | Get-Member | ? {$_.Name.IndexOf('_') -eq -1}

But this would leave other members out (e.g. __NounName) so I changed it to:

Get-Process | Get-Member | ? {$_.Name.IndexOf('_') -lt 1}

But I would still miss some members so I went for the more precise stuff:
Get-Process | Get-Member | ? {$n = $_.Name; -not $n.StartsWith('get_') -and -not $n.StartsWith('set_') -and -not $n.StartsWith('add_') -and -not $n.StartsWith('remove_')}

I then decided to send it to an internal distribution list dedicated to PowerShell asking for any help to make it shorter and/or faster. Alex answered with the following:

… | gm | ?{ !($_.Name -match "^(get|set|add|remove)_") }

I replied that it was indeed shorter but slower. Pressing the Send button, I thought “Never say such things without measuring”. But I’m lazy…

17 minutes later, he answered again:

1..100 | measure-command { ls | … } gives 5.34 sec for your version and 4.72 for mine.

If you think that the file system caching might have something to do with those results, try with processes: his solution is still faster.

Thanks Alex!

> 1..100 | measure-command { get-process | gm | ?{ !($_.Name -match "^(get|set|add|remove)_") } }

Days : 0

Hours : 0

Minutes : 0

Seconds : 13

Milliseconds : 353

Ticks : 133534572

TotalDays : 0.000154553902777778

TotalHours : 0.00370929366666667

TotalMinutes : 0.22255762

TotalSeconds : 13.3534572

TotalMilliseconds : 13353.4572

> 1..100 | measure-command { get-process | gm | ? {$n = $_.Name; -not $n.StartsWith('get_') -and -not $n.StartsWith('set_') -and -not $n.StartsWith('add_') -and -not $n.StartsWith('remove_')} }

Days : 0

Hours : 0

Minutes : 0

Seconds : 15

Milliseconds : 536

Ticks : 155367665

TotalDays : 0.000179823686342593

TotalHours : 0.00431576847222222

TotalMinutes : 0.258946108333333

TotalSeconds : 15.5367665

TotalMilliseconds : 15536.7665