þÿfunction Debug-Regex {

<#

.SYNOPSIS

A very simple function to debug a Regex search operation and show any 'Match' 

results. (V2.1 Export Alias db & some patterns, 28 Jan 2012).



.DESCRIPTION

Sometimes it is easier to correct any regex usage if each match can be shown 

in context. This function will show each successful result in a separate 

colour, including the strings both before and after the match. Using the -F

switch will allow only the first of any matches to be returned.

Commonly used regex patterns may be added to this module, 'exported' and then 

assigned to a variable before being passed to the function. (They can also be

used with the Select-String Cmdlet).



.EXAMPLE

Debug-Regex '\b[A-Z]\w+' 'Find capitalised Words in This string' -first

Use the -F switch to return only the first match. Produces the following...



MATCHES  ---------------<match>--------------------

1 [<Find> capitalised Words in This string]

.EXAMPLE

Debug-Regex '\b[0-9]+\b' 'We have to find numbers like 123 and 456 in this'

Produces the following...



MATCHES  ---------------<match>--------------------

1 [We have to find numbers like <123> and 456 in this]

2 [We have to find numbers like 123 and <456> in this]



.EXAMPLE

PS >$a = Get-Variable regexDouble -ValueOnly

PS >db $a 'Find some double words words in this this string'

Assign the desired Regex string to $a and use this and the alias as parameters.

 

.NOTES

Based on a suggestion from the book 'Mastering Regular Expressions' by J.Friedl,

page 429.



.LINK

   Web Address Http://www.SeaStarDevelopment.BraveHost.com 

#>

   param ([Parameter(mandatory=$true)][regex]$regex,

          [Parameter(mandatory=$true)][string]$string,

          [switch]$first)

   $m = $regex.match($string)

   if (!$m.Success) {

      Write-Host "No Match using Regex '$regex'" -Fore Yellow

      return

   }

   $count = 1

   Write-Host "MATCHES  --------------------<" -Fore Yellow -NoNewLine

   Write-Host "match"                          -Fore White  -NoNewLine

   Write-Host ">--------------------"          -Fore Yellow

   while ($m.Success) {

      Write-Host "$count $($m.result('[$`<'))" -Fore Yellow -NoNewLine 

      Write-Host "$($m.result('$&'))"          -Fore White  -NoNewLine 

      Write-Host "$($m.result('>$'']'))"       -Fore Yellow 

      if ($first) {

         return

      }

      $count++

      $m = $m.NextMatch()

   }

}

# Use a CSV file for larger collections of variables if necessary.



Set-Variable -Name regexDouble  -value '\b(\w+)((?:\s|<[^>]+>)+)(\1\b)' `

             -Description 'Find double word pairs within <>'

Set-Variable -Name regexNumbers -value '\b[0-9]+\b' `

             -Description 'Find only numbers in a string'



New-Alias db Debug-Regex

Export-ModuleMember -Function Debug-Regex -Variable regex* -Alias db