Regular expression is a powerful tool, and it can save lots of lines codes sometimes.
What is Regex
Regex(Regular Expression) describes a pattern of a certain amount of text, so it can be used for string editing.
Online tool
Not sure if your Regex works? Try Regex101, it can make your Regexes much easier.
I also recommend Regular Expression Info, it explains all details that you need to know.
Cheat Sheet
| Character | Meaning | Example |
|---|---|---|
| ^ | the beginning of the string | |
| $ | the end of the string | |
| \b | whole word only | \babc\b matches 'abc', but not 'abcc ' |
| \B | if the pattern is fully surrounded by word | \Babc\B mathes 'aabcc', but not 'abc' |
| . | anything | |
| \d | single digit in 0-9 | |
| \D | single non-digit | |
| \w | single word character | |
| \W | single non-word | |
| \s | white space(space, tab, return, new line) | |
| \S | non-whitespace | |
| \t | tab | |
| \r | return | |
| \n | new line | |
| \g | global search, which means it doesn't stop at the first match | |
| * | zero or more of the previous | abc* matches a string that has ab followed by zero or more c |
| + | one or more of the previous | abc+ matches a string that has ab followed by one or more c |
| ? | zero or one of the previous | abc? matches a string that has ab followed by zero or one c |
| ?: | non-capturing group | |
| X{m} | number of X === m | |
| X{m,} | m < number of X | |
| X{m, n} | m < number of X < n | |
| (X | Y) | X or Y | |
| [...] | any of characters in the class | [abcd] matches a string that has one of the char (a, b, c, d) |
| - | range | [a-d] same as above |
Key words from the cheat sheet
Anchor
Anchor is not a pattern, it is a position.
It matches a position before, after or between characters.
For example, ^ is the beginning of the string, and it is also a start of line anchor.
Boundaries
\b is a word boundary because \babc\b has to match the whole word abc.
\B is non-word-boundary because \Babc\B means any words that includes abc (abcc, eabc).
Quantifiers
Greedy: The optional item is included in the match if possible. ? is a typical example of greedy quantifiers. abc? can match either abc or ab.
Lazy: The optional item is excluded in the match if possible. ?? is a typical one because abc?? only matches ab.
Here is the best example from stack overflow - https://stackoverflow.com/questions/2301285/what-do-lazy-and-greedy-mean-in-the-context-of-regular-expressions
Non-capturing group
?: means the pattern doesn't capture to the group. It usually uses with .match(). So if you use ?:, then the pattern won't be included to the array.
Example from stack overflow -
https://stackoverflow.com/questions/3512471/what-is-a-non-capturing-group-in-regular-expressions
Hope this post helps ❤️
Top comments (3)
Thanks for sharing this article. Just wanted to share that if at all someone is looking for readymade patterns, I have found regexr.com/ very much useful. It has a section called "Community Patterns" where one can avail of tons of ready-made patterns and customize if required. 😀
Hello and thanks for the post, as per online tools I will add also:
webperl.zero-g.net/regex.html (powered by webperl so still beta but fully functioning)
retester.herokuapp.com/
debuggex.com/
And the deep and useful rexegg.com/
Thank you for the post.
I use regex a lot in my work. It's very helpful and once you start understanding and using it, it becomes more clear. many developers are afraid of regex but please don't be.