Strange unstopable Do-While cycle in Powershell

Question

I have a strange problem. Want to create a script that input user to insert a string and than loop again in the input request until leaved blank.

The script work well in PowerGUI continuing prompting a input request until i press only [Enter] than the script go on. The problem appear when i try to use the script on a powershell shell. Pressing only [Enter] let the DoWhile cycle continue to prompt me the input request without possibility to stop it unless CTRL-Z it.

Some ideas to why?

[Int] $num = 1
[Array] $conts = @()

do {
    $a = read-host "Indirizzo mail Contatto $num`?"
    if ($a -ne $null) {
            $num++
            $conts += $a
    } 

} while($a -ne $null)

Function CreaContatto {
    $mailContact = $args 
    $aliasContact = $args -replace ("@","_")
    New-MailContact -ExternalEmailAddress $mailContact -Name $mailContact -Alias $aliasContact
}

ForEach ($cont in $conts) {CreaContatto $cont}

Mike Zboray · Accepted Answer · 2015-02-06 16:00:58Z

2

My guess is that PowerGUI implements a custom host and that returns null from read-host when there is no input. The standard PowerShell host doesn't do that, it returns an empty string (unless you hit ctrl-z which signals end-of-file). Since both are falsy you can do this:

do {
    $a = read-host "Indirizzo mail Contatto $num`?"
    if ($a) {
        $num++
        $conts += $a
    }
} while($a)

answered Feb 6, 2015 at 16:00

Mike Zboray

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1 Comment

smark91 Over a year ago

Many thanks. You are right about PowerGUI return. Analysing the variable value during the script run your supposition are right. PowerGUI assign the $null value when string are empty. Probably Powershell doesn't do.

arco444 · Accepted Answer · 2015-02-06 15:56:49Z

2

Thing is, $a is not null when pressing Enter, it is a newline. You can see this if you add a write-host $a below your if statement.

In this case, I'd suggest using a regex:

do {
    $a = read-host "Indirizzo mail Contatto $num`?"
    if ($a -ne $null) {
            $num++
            $conts += $a
    } 

} while($a -match '.+')

This says that $a has to be one or more characters.

answered Feb 6, 2015 at 15:56

arco444

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1 Comment

smark91 Over a year ago

Your answer is right but for simplicity I choose the "mike z" one. Need to implement more right answer on StackOverflow.

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