Parsing text with regular expressions in C#.

The first thing you need to test regular expression patterns is a Regex tester like regex101.com.

Patterns

The Regex engine in .NET (System.Text.RegularExpressions) evaluates a string like 20 goto 1 with a pattern like \d{0,1}. In this case the regex finds 2 matches: 10 and 20 because:

• \d is a decimal
• {0,1} takes either 1 or 2 decimals

{0,1} is called a greedy pattern, which means it will return 20 instead of 2 and 0.

in C# it would look like this:

var input = "20 goto 1";
var pattern = @"\d{1,2}";
var match = Regex.Match(input, pattern);

It’s simple and powerful once you get it. I will add regex patterns to this post as I use them.

Find 1-or-2-digit decimal numbers in text

This pattern finds all occurrences of numbers between 0 and 99 in text:

\d{1,2}

Find all tags (#tag) in text

Pattern:

#(\w+)

Input:

this is a #tag and another #tag

Match information:

Match 1
Full match	10-14	`#tag`
Group 1.	11-14	`tag`

Match 2
Full match	27-31	`#tag`
Group 1.	28-31	`tag`

Match if string starts with time in 24-hour format

Pattern:

^([0-9]|[0-2][0-9]):([0-5][0-9])

Input:

12:00 Schloßpark Köpenick (until 19:00)

Match information:

Match 1
Full match	0-5	`12:00`
Group 1.	0-2	`12`
Group 2.	3-5	`00`