Powershell - 在循环、变量初始化和 if 语句中调用 function

Question

Like the title said, I have some trouble using functions in loops, variable initialisation and if statements as conditions. However, if I just call the fuction out of the blue it does work fine, leading me to think the problem is how I call the function and not the function itself, I may be wrong though.

Here's the function I'm trying to call:

function checkAlphaNumerical {
    param (
        #First, the string to validate, then a string to append to the error message
        $stringToValidate, $stringDesc
    )
    if ($stringToValidate -notmatch '^[a-z0-9]+$') {
        Write-Output ("Invalid $($stringDesc)")
        return $false
    }
    else {
        return $true
    }
}

Since I use return $true and return $false on both possible path of the function, Powershell console should output me True or False depending on the string value.

Here's the only scenario where calling the function works:

checkAlphaNumerical $testinput "test"

Here's three example where it does not work:

 do {
    $testinput = Read-Host -Prompt "Enter string"
} while (!(checkAlphaNumerical $testinput "test"))

 if (checkAlphaNumerical $testinput "test") {
            #stuff
        }

$someBool = checkAlphaNumerical $testinput "test"

Thanks in advance for your help.

Answer 1

It's not working as expected because your function, as written, returns a two-element object array when your test is false:

PS > $TestFailure = checkAlphaNumerical '%' "FailTest"
PS > $TestFailure
Invalid FailTest
False
PS > $TestFailure.GetType()

IsPublic IsSerial Name                                     BaseType
-------- -------- ----                                     --------
True     True     Object[]                                 System.Array


PS > $TestFailure[0]
Invalid FailTest
PS > $TestFailure[1]
False
PS > [bool]$TestFailure
True
PS keith>

And when the array is cast as a boolean, as it is when serving as a test conditon, it returns $True .

Changing write-Output to Write-Warning will display your "Invalid...." message at the console while ensuring the return value is simply $False . Also:

• In PowerShell functions, the Return statement is unnecessary. Any unconsumed output is returned.
• Since $stringDesc is simply a string variable, you don't need "...$($stringDesc)" in your expansion string.

So a working version of your fucntion would be:

function checkAlphaNumerical {
    param (
        #First, the string to validate, then a string to append to the error message
        $stringToValidate, $stringDesc
    )
    if ($stringToValidate -notmatch '^[a-z0-9]+$') {
        Write-Warning ("Invalid $stringDesc")
        $false
    }
    else {
        $true
    }
}

Output:

PS > do {
>>     $testinput = Read-Host -Prompt "Enter string"
>> } while (!(checkAlphaNumerical $testinput "test"))
Enter string: '%'
WARNING: Invalid test
Enter string: '?'
WARNING: Invalid test
Enter string: abc
PS >