Debug regex operation when matching any string

Share |

Browse Library

Tags

Previous | Next | View all files | View Slideshow

Download

posted by Archdeacon

01-25-2012

Downloads: 55

File size: 5.6kB

Embed

Debug regex operation when matching any string

function 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 

Filed under: Powershell, Regular Expressions

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