Regular Expressions
Regular expressions are extremely useful in extracting information from text such as code, log files, spreadsheets, or even documents. The first thing to recognize when using regular expressions is that everything is essentially a character, and we are writing patterns to match a specific sequence of characters (also known as a string).
Generally, the key part to process the text with regular expressions is regular expression engine and it is represented by Regex
class in c#. The Regex
class is available with System.Text.RegularExpressions namespace.
abc… | Letters |
123… | Digits |
\d | Any Digit |
\D | Any Non-digit character |
. | Any Character |
\. | Period |
[abc] | Only a, b, or c |
[^abc] | Not a, b, nor c |
[a-z] | Characters a to z |
[0-9] | Numbers 0 to 9 |
\w | Any Alphanumeric character |
\W | Any Non-alphanumeric character |
{m} | m Repetitions |
{m,n} | m to n Repetitions |
* | Zero or more repetitions |
+ | One or more repetitions |
? | Optional character |
\s | Any Whitespace |
\S | Any Non-whitespace character |
^…$ | Starts and ends |
(…) | Capture Group |
(a(bc)) | Capture Sub-group |
(.*) | Capture all |
(abc|def) | Matches abc or def |
Example
Following is the example of validating whether the given text is in proper email format or not using Regex
class in C#.
C# Regex Class Methods
Method | Description |
IsMatch | It will determine whether the given input string matching with regular expression pattern or not. |
Matches | It will return one or more occurrences of text that matches the regular expression pattern. |
Replace | It will replace the text that matches the regular expression pattern. |
Split | It will splits the string into an array of substrings at the positions that matches the regular expression pattern. |
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