I'm often asked by folks if there's a "better way" to do something in a script. Often times, they're looking for a better procedural approach - following best practices like object-based output, for example. But sometimes, they're looking for better performance from a script or command. Well, the good news is that PowerShell itself can help with that.
Let's consider two short scripts that produce almost identical output. Here's the first:
Get-Process |
Select-Object Name,ID,
@{n='PM(KB)';e={$_.pm / 1kb -as [int]}},
@{n='VM(KB)';e={$_.vm / 1kb -as [int]}} |
Where { $_.Name -like 's*' } |
Format-Table -AutoSize
Which outputs the following:
Name Id PM(KB) VM(KB)
---- -- ------ ------
SearchIndexer 2400 16332 511936
services 532 3700 34296
smss 292 272 4276
spoolsv 1060 3688 55996
svchost 264 12980 93388
svchost 644 2132 38588
svchost 684 2428 31988
svchost 756 10192 1414100
svchost 768 15724 104180
svchost 896 23096 589812
svchost 976 5064 87876
svchost 1100 12528 348288
svchost 2172 5056 94256
System 4 120 4196
Now consider this second version:
Get-Process -Name s* |
Format-Table Name,ID,
@{n='PM(KB)';e={$_.pm};formatstring="N2"},
@{n='VM(KB)';e={$_.vm};formatstring="N2"} -AutoSize
And its output:
Name Id PM(KB) VM(KB)
---- -- ------ ------
SearchIndexer 2400 16,723,968.00 524,222,464.00
services 532 3,788,800.00 35,119,104.00
smss 292 278,528.00 4,378,624.00
spoolsv 1060 3,776,512.00 57,339,904.00
svchost 264 13,295,616.00 95,629,312.00
svchost 644 2,183,168.00 39,514,112.00
svchost 684 2,539,520.00 33,288,192.00
svchost 756 10,436,608.00 1,448,038,400.00
svchost 768 16,326,656.00 108,277,760.00
svchost 896 15,773,696.00 449,454,080.00
svchost 976 5,132,288.00 89,452,544.00
svchost 1100 12,881,920.00 357,179,392.00
svchost 2172 4,464,640.00 94,494,720.00
System 4 122,880.00 4,296,704.00
Again, same data, just a different way of getting it. The second one is a bit prettier, too. So is there a performance difference? PowerShell's Measure-Command approach can tell us. I've saved these in script files named First.ps1 and Second.ps1, mainly for convenience; it's completely legitimate to ask Measure-Command to measure a command, rather than a script file, but when the commands get complex I find them easier to read in a script.
PS C:\> measure-command -Expression { C:\first.ps1 }
Days : 0
Hours : 0
Minutes : 0
Seconds : 0
Milliseconds : 82
Ticks : 825043
TotalDays : 9.5491087962963E-07
TotalHours : 2.29178611111111E-05
TotalMinutes : 0.00137507166666667
TotalSeconds : 0.0825043
TotalMilliseconds : 82.5043
PS C:\> measure-command -Expression { C:\second.ps1 }
Days : 0
Hours : 0
Minutes : 0
Seconds : 0
Milliseconds : 87
Ticks : 871232
TotalDays : 1.00837037037037E-06
TotalHours : 2.42008888888889E-05
TotalMinutes : 0.00145205333333333
TotalSeconds : 0.0871232
TotalMilliseconds : 87.1232
Holy smokes. The first one was faster. OK, only by 5 milliseconds, but it was faster! And the first one doesn't exactly use what I'd call "best practices." It's filtering out processes whose names don't start with "S" way late in the game - after doing all that Select-ing. It's possible that the second script's Format-Table, with all that FormatString fanciness, is what's making the second script run longer. Fortunately, we can now go in and start tweaking things around, re-testing, and even testing individual commands to get the script running as fast as possible. I'll leave that to you, for these two examples - how fast can you get one to run while producing substantially the same output?
Measure-Command is a useful tool, but always remember that it's really running your script. This isn't some kind of testing mode (and if you run commands with -WhatIf, you won't get the same performance results). So you'll often want to test this in a virtual environment, getting your command fine-tuned and read for production.