Extract value from powershell regex matches

Question

As a part of a buildscript in powershell, I am trying to extract a version number from a string using regular expression. The number is assumed to be in a format xx.yy (eg. 10.6) I need the Integer part (in this example, it would be 10) and the fraction part (example: 6)

I want to have a method that checks that both my patterns exists and thereafter extracts the numbers. (I am very much a novice in powershell, and am trying to avoid using C# functions, but rather powershell itself.)

I tried to do this:

$integralPart="A"
$fractionPart="B"

function GetVersion {
    param([string]$strVersion)
    $integralPattern="^[0-9]+(?=\.)" 
    $fractionalPattern="(?<=\.)[0-9]+$"

    #Check if string consists of an integral and fractional part
    If ($strVersion -match $integralPattern -eq $True -and $strVersion -match $fractionalPattern -eq $True)
    {
        $strVersion -match $integralPattern
        $integralPart = $matches[0]

        $strVersion -match $fractionalPattern
        $fractionalPart = $matches[0]
    } 
    else
    {
        Write-Host "You did not enter a double with an integer and a fractional part (eg. 10.6)"
        Exit
    }
}

GetVersion (Read-Host 'Enter program version')
Write-Host $integralPart
Write-Host $fractionPart

In doing so, I was hoping that $integralPart and $fractionalPart would contain my numbers, at they match the values they should

Can anyone explain how this can be done?

The problem is that the variables inside the function are not the ones you have declared at the top. Use solutions from [powershell setting a global variable from a function where the global variable name is a variable passed to the function](http://stackoverflow.com/questions/12535419/powershell-setting-a-global-variable-from-a-function-where-the-global-variable-n) — Wiktor Stribiżew, Jan 13 '16 at 21:35
Ah, should have checked. $matches[0] actually DOES contains the right values.... but i must still do something wrong, as $integralPart and $fractionPart still end up with the values they were intitialized with — Bo Visfeldt, Jan 13 '16 at 21:42

score 3 · Accepted Answer · answered Jan 13 '16 at 21:59

3

You need to tell PS that the variables are from global scope with $global:

$integralPart="A"
$fractionPart="B"

function GetVersion {
    param([string]$strVersion)
    $integralPattern="^[0-9]+(?=\.)" 
    $fractionalPattern="(?<=\.)[0-9]+$"

    #Check if string consists of an integral and fractional part
    If ($strVersion -match $integralPattern -eq $True -and $strVersion -match $fractionalPattern -eq $True)
    {
        $strVersion -match $integralPattern
        $global:integralPart = $matches[0]   // SEE HERE

        $strVersion -match $fractionalPattern
        $global:fractionPart = $matches[0]   // SEE HERE
    } 
    else
    {
        Write-Host "You did not enter a double with an integer and a fractional part (eg. 10.6)"
        Exit
    }
}

GetVersion "10.6"
Write-Host $integralPart
Write-Host $fractionPart

Output:

True
True
10
6

Also, you have a typo: inside the GetVersion, you have $fractionalPart while the global variable is called $fractionPart.

answered Jan 13 '16 at 21:59

Wiktor Stribiżew

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For things like this I'm a fan of casting the RegEx pattern as a `[RegEx]` type, and then doing a `$global:integralPart = $integralPattern.Matches($strVersion).value` kind of thing. Saves you the extra "True" output. – TheMadTechnician Jan 13 '16 at 22:06
@TheMadTechnician: I see but that would require some more changes with the code, I am not sure OP wants that. BTW, I think you meant `.Match` (not `.Matches`). @Bo Visfeldt: Does that work all right for you? – Wiktor Stribiżew Jan 13 '16 at 22:37
Instead of using globals you could save yourself a lot of future pain by adding the variables as parameters to the function. This also increases the functions reusability. – Bluecakes Jan 13 '16 at 23:10
Actually, I did mean Matches. The Match method only tells you True/False if it does match. The Matches method actually specifies what the matching substring is instead of doing Match, and then using the `$Matches` automatic variable. – TheMadTechnician Jan 13 '16 at 23:37
@TheMadTechnician: Ok, but it does not have `Value` property. It would be necessary to access the first match using the 0th index. – Wiktor Stribiżew Jan 13 '16 at 23:38
I beg to differ. Run `'ab12cd','ef34gh','ij56kl'|%{([regex]"\d{2}").matches($_).value}` and it will successfully extract the two digit number from the three strings provided. – TheMadTechnician Jan 13 '16 at 23:42

Extract value from powershell regex matches

1 Answers1