It’s the little things

It’s the little things in PowerShell that make a rigid C# developer smile… In the following example, I distribute an array result to separate variables in one line.

$NPA,$NXX,$Digits = Split-Phone 202-456-1111

# In C#, the equivalent would be
# string[] results = SplitPhone("202-456-1111");
# string npa = results.Length > 0 ? results[0] : null;
# string nxx = results.Length > 1 ? results[1] : null;
# string digits = results.Length > 2 ? results[2] : null;

And even the C# syntax mentioned above doesn’t exactly do the same thing because in PowerShell, if the array contains more elements than you’re distributing, the last variable can receive the “remainder” of the array. Since C# doesn’t really have a concept of singleton arrays being treated as strings, there is no direct analogy.

##############################################################################
#.SYNOPSIS
# Splits a phone number into NPA, NXX, and 4 digit components.
#
#.PARAMETER TN
# The telephone number to split.
#
#.RETURNVALUE
# If the specified number is a valid US telephone number, the return value is
# a 3 element array containing NPA, NXX, and the 4 digit line. Otherwise, an
# exception is thrown.
##############################################################################
function Split-Phone {

    param ( [String]$TN )

    
    $Pad = '\s*'
    $Sep = '(\s+|\.|\-)?'
    $Intl = '(?<intl>\+?1)?'
    $NPA = '(\s*\(?\s*(?<npa>\d{3})\s*\)?\s*)'
    $NXX = '(?<nxx>\d{3})'
    $Digits = '(?<digits>\d{4})?'
    
    $Pattern = "^$Pad$Intl$Sep$NPA$Sep$NXX$Sep$Digits$Pad`$"
    
    Write-Debug "Split-Phone Pattern: $Pattern"
    
    if ( $TN -match $Pattern ) {
        if ( $Matches['digits'] ) {
            @(  $Matches['npa'],
                $Matches['nxx'],
                $Matches['digits'] )
        }
        else {
            @(  $Matches['npa'],
                $Matches['nxx'] )
        }
    }
    else {
        throw "Invalid TN: $TN" 
    }
       
}