DevTut

# Regex Parsing

# Single match

using System.Text.RegularExpressions;

string pattern = ":(.*?):";
string lookup = "--:text in here:--";

// Instanciate your regex object and pass a pattern to it
Regex rgxLookup = new Regex(pattern, RegexOptions.Singleline, TimeSpan.FromSeconds(1));
// Get the match from your regex-object
Match mLookup = rgxLookup.Match(lookup);

// The group-index 0 always covers the full pattern.
// Matches inside parentheses will be accessed through the index 1 and above.
string found = mLookup.Groups[1].Value;

Result:

found = "text in here"

# Multiple matches

using System.Text.RegularExpressions;

List<string> found = new List<string>();
string pattern = ":(.*?):";
string lookup = "--:text in here:--:another one:-:third one:---!123:fourth:";

// Instanciate your regex object and pass a pattern to it
Regex rgxLookup = new Regex(pattern, RegexOptions.Singleline, TimeSpan.FromSeconds(1));
MatchCollection mLookup = rgxLookup.Matches(lookup);

foreach(Match match in mLookup)
{
    found.Add(match.Groups[1].Value);
}

Result:

found = new List<string>() { "text in here", "another one", "third one", "fourth" }

# Syntax

  • new Regex(pattern); //Creates a new instance with a defined pattern.
  • Regex.Match(input); //Starts the lookup and returns the Match.
  • Regex.Matches(input); //Starts the lookup and returns a MatchCollection

# Parameters

Name Details
Pattern The string pattern that has to be used for the lookup. For more information: msdn (opens new window)
RegexOptions [Optional] The common options in here are Singleline and Multiline. They are changing the behaviour of pattern-elements like the dot (.) which won't cover a NewLine (\n) in Multiline-Mode but in SingleLine-Mode. Default behaviour: msdn (opens new window)
Timeout [Optional] Where patterns are getting more complex the lookup can consume more time. This is the passed timeout for the lookup just as known from network-programming.

# Remarks

Needed using

using System.Text.RegularExpressions;

Nice to have

Especially beginners are tended to overkill their tasks with regex because it feels powerful and in the right place for complexer text-based lookups. This is the point where people try to parse xml-documents with regex without even asking theirselfes if there could be an already finished class for this task like XmlDocument.

Regex should be the last weapon to pick agains complexity. At least dont forget putting in some effort to search for the right way before writing down 20 lines of patterns.

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