Powershell

Please provide some more information what it is exactly you want to do.
Well, for an email address, you can check whether the string contains a "@" and at least one dot behind it.
But how do you define "alias", and how can you differentiate it from from a "display name" in your scenario?

Do you want to check against Active Directory entries to validate the input?

Sindhura, please reply in your question, not as messages.

Thanks for your quick response. Let's say, an input can be determined as      

      email address if it contains "@" and ".com"
      alias if it contains "." like first name.last name
      display name if it contains "," like lastname, first name

As a quick draft (the regexes could be refined) to check if this resembles what you need:

$Input = Read-Host -Prompt "Input"
Switch -regex ($Input) {
	'.+@.+\.com' {$Type = 'Email'; Break}
	'.+,\s*.+' {$Type = 'Display'; Break}
	'.+\..+' {$Type = 'Alias'; Break}
	default  {$Type = 'Unknown'; Break}
}
Write-Host "Type: $($Type)"

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Thanks a lot, it works in desired manner

Could you please explain me the below expressions. I do understand that "," and "." are used here to identify the inputs as display name and alias respectively.

'.+,\s*.+' {$Type = 'Display'; Break}
'.+\..+' {$Type = 'Alias'; Break}

These are "Regular Expressions" (see, for example, http://www.regular-expressions.info/quickstart.html ).
A single "." is any character, the "+" behind it means at least one, "\s" is a space the "*" behind it means 0 or any number of repetitions.
The escaped dot, "\.", is a literal ".".

I have gone through the provided article and got a clear understanding of regular expressions. Checked them with few test expressions as well.

I am currently working on a powershell script which should meet the below requirements:

                       Input is a file which consists of a complete list of email addresses or alias or display name
                       Script should identify if the input is email addresses or alias or display name
                       Script should prompt user to select output which could be any attribute of the command "get-mailbox -identity <>"
                       User enters the attributes names which he/she desires and it could be 1, 2 or many attributes
                       If mailbox i.e., input doesn't exist, then the attribute result should be "Not Found"

I have worked on the same scenario with single user as input:

$UserInputName = Read-Host "`t`tPlease enter the user"
$AttributeInput = Read-Host "`t`tPlease enter the required attribute"
get-mailbox -identity $UserInputName | select $AttributeInput

Could you please assist me on the last 2 steps of script:

                       1. Input is a file which consists of a complete list of email addresses or alias or display name
                       2. Script should identify if the input is email addresses or alias or display name
                       3. Script should prompt user to select output which could be any attribute of the command "get-mailbox -identity <> | fl"
                       4. User enters the attributes names which he/she desires and it could be 1, 2 or many attributes
                       5. If mailbox i.e., input doesn't exist, then the attribute result should be "Not Found"

Input here will be a file which consists f number of users
And the desired output is any of the attributes of the command "get-mailbox -identity <> | fl"

As before, can't test the Get-Mailbox part, but it works with Get-ADUser.

$UserFile = 'C:\Temp\Users.txt'
$OutputFile = 'C:\Temp\Export.csv'
$AttributeInput = Read-Host "`t`Please enter the required attribute(s) (a comma separated list is possible)`r`n`t"
$AttributeList = @($AttributeInput.Split(',') | ForEach-Object {$_.Trim()})
Write-Host "Attributes:"
$AttributeList | ForEach-Object {Write-Host "`t - $($_)"}
Get-Content -Path $UserFile | ForEach-Object {
	$Identifier = $_
	Write-Host "Processing '$($Identifier)' ..." -NoNewline
	Switch -regex ($Identifier) {
		'.+@.+\.com' {$Type = 'Email'; Break}
		'.+,\s*.+' {$Type = 'Display'; Break}
		'.+\..+' {$Type = 'Alias'; Break}
		default  {$Type = 'Unknown'; Break}
	}
	Write-Host " type is $($Type)."
	Try {
		$Mailbox = Get-Mailbox -Identity $Identifier -ErrorAction Stop
	} Catch {
		$_.Exception.Message | Write-Host -Fore Red
		$Mailbox = '' | Select-Object -Property $AttributeList
		$AttributeList | ForEach-Object {$Mailbox.$_ = 'n/a'}
	}
	$Mailbox | Select-Object (@(@{Name='Identifier'; Expression={$Identifier}}) + $AttributeList)
} | Export-Csv -NoTypeInformation -Path $OutputFile

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Sin Ga, I'm not amused about https://www.experts-exchange.com/questions/28980973/Powershell-script.html - which is a very similar question, and I've supplied you with a comfortable attribute choice there. The question is still open.

I cannot see why determining which kind of data has been supplied has any relevance but for display, so strictly seen this two questions are duplicates.

I am really sorry, I did not check your comment over there. If I have seen, I would have replied there itself. Since the requirements of the script has changed, I have created a new post. I am really grateful for your assistance on this.

      I believe, it has to be Write-Host "$AttributeList" instead of Write-Host "Attributes:" in the script so that is displays the attributes selected by the user.

Thanks a lot again and so sorry for the double posts.

Best solution

I believe, it has to be Write-Host "$AttributeList" instead of Write-Host "Attributes:" in the script so that is displays the attributes selected by the user.

No. That line is just decoration. The attributes identified will be listed below that line, each attribute in its own line, with the next line of code:

$AttributeList | ForEach-Object {Write-Host "`t - $($_)"}

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