Learn Regular Expressions using Atom

This is a short little post with the goal of helping you to learn the elusive regular expressions!

This takes advantage of a built in regex feature in the Atom text editor. It may work in other text editors as well, so give it a try in your favorite text editor or IDE. If it doesn’t work, you can download Atom here (don’t worry, its free!).

Tutorial

First, create a new file in the Atom editor.

Next, type in a line of text. Here is the line I will be using (Hello). [World!].

Next type CMD+f (Ctrl+f on Windows) to open the find and replace utility.

Then select the ‘regex’ option to treat the search item as a regular expression (see red arrow below).

Image of Atom Regex Option
Atom Regex Option

Finally, highlight the line of text that you typed and press CMD+f (Ctrl+f on Windows). The search box should update to display your selection formatted as a regular expression.

Image of Atom Regex in 'find and replace' utility
Regex in Atom ‘find and replace’ utility

Congratulations!  You now know how to use Atom to build regular expressions for you!

Understanding the generated expression

Recall that the original string was (Hello). [World!].  Parenthesis and brackets are special symbols in regex, so they must be escaped with the \ character.  Note that a period . is also a special regex character.  This is one of the most misused characters in regex, because a period by itself will match any character!  Simply typing a . to match a period in a string will match that string, but it will also match any string that contains any other character in place of the period.

Limitations

This only works for one-line expressions. 🙁  Even magic has its limits :).

Additional links

https://regexone.com/ – An awesome interactive tutorial for learning regular expressions.

https://regex101.com/ – A regex tester. You must know the regular expression, or try typing regular expressions until they match the example text you entered.