Category Archives: regular expressions

Use string extension methods to validate Social Security numbers in C#

Posted on June 19, 2017 by Rod Stephens

This example defines three extension methods that return true if strings contain Social Security numbers. Recall that you must add extension methods to a static class and that the methods must be static. This example begins by defining a Matches … Continue reading →

Posted in extension methods, extensions, regular expressions, strings | Tagged C#, C# programming, example, example program, extension methods, extensions, regular expressions, Social Security numbers, strings, Windows Forms programming | 5 Comments

Move a window with a title that matches a pattern in C#

Posted on December 27, 2016 by Rod Stephens

The example Set another application’s size and position in C# uses the FindWindow API function to find a window with a given title. Unfortunately FindWindow only finds the window if the title is an exact match. If you only know … Continue reading →

Posted in API, miscellany, regular expressions, system | Tagged API, C#, C# programming, EnumDesktopWindows, example, example program, find desktop window, find window, miscellany, regular expressions, system, window, Windows Forms programming | Leave a comment

Remove non-digits or non-letters from a string in C#

Posted on April 11, 2015 by Rod Stephens

Sometimes you might want to extract only the digits, letters, or some other group of characters from a string. You could loop through the string examining each character individually. Fortunately there’s a much easier way to do this. The regular … Continue reading →

Posted in parsing, regular expressions, strings | Tagged alpha numeric strings, alpha strings, C#, C# programming, example, example program, non-digits, non-letters, numeric strings, only digits, only letters, parsing, regular expressions, replace, strings, Windows Forms programming | 2 Comments

List unique words in a text file in C#

Posted on January 5, 2015 by Rod Stephens

This example uses regular expressions and LINQ to list the unique words contained in a text file in C#. When you enter the name of a file and click List Words, the following code executes. // List the words in … Continue reading →

Posted in files, LINQ, regular expressions | Tagged C#, C# programming, count words, example, example program, files, find words, LINQ, regular expressions, unique words, Windows Forms programming | 1 Comment

Understand C# regular expression symbols

Posted on November 5, 2014 by Rod Stephens

The following table shows useful regular expression symbols, commands, and other items that you can use in regular expressions in C# programs. Item Purpose \ Either begins a special symbol such as \n or escapes the following character ^ Matches … Continue reading →

Posted in regular expressions, strings | Tagged C#, C# programming, example, example program, matching, pattern matching, pattern replacements, regular expression symbols, regular expressions, replacements, strings, Windows Forms programming | Leave a comment

Replace text in the lines of a string in C#

Posted on November 5, 2014 by Rod Stephens

This example uses the following code to replace text in the lines of a string. private void btnGo_Click(object sender, EventArgs e) { try { Regex reg_exp = new Regex(txtPattern.Text); lblResult.Text = reg_exp.Replace( txtInput.Text, txtReplacementPattern.Text); } catch (Exception ex) { MessageBox.Show(ex.Message); … Continue reading →

Posted in regular expressions, strings | Tagged C#, C# programming, example, example program, parse, parsing, patterns, regular expressions, replace, replace lines, string parsing, strings, Windows Forms programming | 6 Comments

Replace text matching a pattern in C#

Posted on November 5, 2014 by Rod Stephens

This example uses the following code to replace text matching a pattern within a string. // Make the replacements. private void btnGo_Click(object sender, EventArgs e) { Regex reg_exp = new Regex(txtPattern.Text); lblResult.Text = reg_exp.Replace( txtTestString.Text, txtReplacementPattern.Text); } This code creates … Continue reading →

Posted in regular expressions, strings | Tagged C#, C# programming, example, example program, pattern matching, pattern replace, regular expressions, replace, replace strings, replace substrings, strings, Windows Forms programming | Leave a comment

Show regular expression matches in C#

Posted on November 5, 2014 by Rod Stephens

When you click the Go button, the program uses the following code to display regular expression matches in a string. Regex reg_exp = new Regex(txtPattern.Text); MatchCollection matches = reg_exp.Matches(txtTestString.Text); rchResults.Text = txtTestString.Text; foreach (Match a_match in matches) { rchResults.Select(a_match.Index, a_match.Length); … Continue reading →

Posted in regular expressions, strings | Tagged C#, C# programming, example, example program, matches, pattern matching, regular expression matches, regular expressions, string matching, strings, Windows Forms programming | Leave a comment

Use regular expressions to rename files within a date range and that match a pattern in C#

Posted on September 12, 2014 by RodStephens

This example extends the example Use regular expressions to rename files that match a pattern in C# to let you rename files within a date range. See the previous example for most of the details. This post describes the changes … Continue reading →

Posted in files, regular expressions | Tagged C#, C# programming, date range, example, example program, file modification date, files, pattern matching, patterns, Regex, regular expressions, rename files, Windows Forms programming | Leave a comment

Use regular expressions to rename files that match a pattern in C#

Posted on September 11, 2014 by Rod Stephens

This example shows how to use regular expressions to rename files. To use the program, enter a directory name and a file pattern. Also enter regular expression find and replace patterns. When you click Preview Changes, the program searches the … Continue reading →