If You Like Regular Expressions So Much, Why Don't You Marry Them?
I'm continually amazed how useful regular expressions are in my daily coding. I'm still working on the MhtBuilder refactoring, and I needed a function to convert all URLs in a page of HTML from relative to absolute:
''' <summary>
''' converts all relative url references
''' href="myfolder/mypage.htm"
''' into absolute url references
''' href="http://mywebsite/myfolder/mypage.htm"
''' </summary>
Private Function ConvertRelativeToAbsoluteRefs(ByVal html As String) As String
Dim r As Regex
Dim urlPattern As String = _
"(?<attrib>shref|ssrc|sbackground)s*?=s*?" & _
"(?<delim1>[""']{0,2})(?!#|http|ftp|mailto|javascript)" & _
"/(?<url>[^""'>]+)(?<delim2>[""']{0,2})"
Dim cssPattern As String = _
"@imports+?(url)*['""(]{1,2}" & _
"(?!http)s*/(?<url>[^""')]+)['"")]{1,2}"
'-- href="/anything" to href="http://www.web.com/anything"
r = New Regex(urlPattern, _
RegexOptions.IgnoreCase Or RegexOptions.Multiline)
html = r.Replace(html, "${attrib}=${delim1}" & _HtmlFile.UrlRoot & "/${url}${delim2}")
'-- href="anything" to href="http://www.web.com/folder/anything"
r = New Regex(urlPattern.Replace("/", ""), _
RegexOptions.IgnoreCase Or RegexOptions.Multiline)
html = r.Replace(html, "${attrib}=${delim1}" & _HtmlFile.UrlFolder & "/${url}${delim2}")
'-- @import(/anything) to @import url(http://www.web.com/anything)
r = New Regex(cssPattern, _
RegexOptions.IgnoreCase Or RegexOptions.Multiline)
html = r.Replace(html, "@import url(" & _HtmlFile.UrlRoot & "/${url})")
'-- @import(anything) to @import url(http://www.web.com/folder/anything)
r = New Regex(cssPattern.Replace("/", ""), _
RegexOptions.IgnoreCase Or RegexOptions.Multiline)
html = r.Replace(html, "@import url(" & _HtmlFile.UrlFolder & "/${url})")
Return html
End Function
Each regex is repeated because I have to resolve relative URLs starting with forward slashes to the webroot first--and then all remaining relative URLs to the current web folder.
One of the BCL team recently recommended pretty-printing regular expressions, eg, using whitespace to make regexes more readable with RegexOptions.IgnorePatternWhitespace. I agree completely. We do this all the time with SQL. I can think of a half-dozen tools that will block of SQL and pretty format it-- but I am not aware of any regex tools that offer this functionality. I guess I'll email the author of Regexbuddy and see what he has to say.
And here's an interesting bit of trivia: did you know that the ASP.NET page parser uses regular expressions?