Powershell: Escape a String for regular expression.

Hi,

when a pattern for a regular expression contains reserved characters it can be difficult to quote all these signs correctly.


A .NET function helps 🙂

Let us assume you want to parse a HTML Site for download links. The lines with the link have the format


<li><a href="http://cert.mydomain.org/pki/Cert0001.crt" target="_blank">download</a></li>

Characters like “.” or Spaces must be escaped. The function Escape() from the RegEx class helps:

$sLink='<li><a href="http://cert.mydomain.org/pki/Cert0001.crt" target="_blank">download</a></li>'
$EscapedString=[System.Text.RegularExpressions.Regex]::Escape($sLink)
$EscapedString

<li><a\ href="http://cert\.mydomain\.org/pki/Cert0001\.crt"\ target="_blank">download</a></li>

And then its simply to extract the download link(all crt files from cert.mydomain.org) :

$sPattern='
<li><a\ href="(http://cert\.mydomain\.org/pki/.+\.crt)"\ target="_blank">download</a></li>

'
[System.Text.RegularExpressions.Regex]::Match($sLink, $sPattern).Groups[1].Value
http://cert.mydomain.org/pki/Cert0001.crt

Michael

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