What is RegEx?
RegEx is shorthand for "regular expression". It defines a pattern for searching or manipulating strings. For example, if you were looking for the word "gray", but wanted to search both possible spellings ("gray" and "grey") with one search, you could use the regular expression `«gr[ae]y» ` to search for both words at once.
How is RegEx Useful?
"So what?" you might be thinking. "Looks like some old-school database stuff."
Well, what if I told you that this regular expression `«\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}\b»` can be used to validate an email?. Imagine all the code it would take to validate an input as an email address without a regex string. Regex is a handy tool to keep in your toolkit as a web developer, especially its `-g` flag to check results globally.
Some other use cases where RegEx's string-matching capabilities can help:
- Validate a domain name: ` $url = "http://abstractapi.com/"; if (preg_match('/^(http|https|ftp)://([A-Z0-9][A-Z0-9_-]*(?:.[A-Z0-9][A-Z0-9_-]*)+):?(d+)?/?/i', $url)) { echo "Your url is ok."; } else { echo "Wrong url."; } `
- Remove ~~repeated words~~ repeated words: ` $text = preg_replace("/s(w+s)1/i", "$1", $text); `
- Find and print the information in the `<title> </title>` tag on a website: ` $fp = fopen("https://abstractapi.com","r"); while (!feof($fp) ){ $page .= fgets($fp, 4096); } $titre = eregi("<title>(.*)</title>",$page,$regs); echo $regs[1]; fclose($fp); `
Regex and JSON
Where is another place we see text in API development? The JSON file. We can validate API responses using Regex:
var body = JSON.parse(context.response.body);
assert( body.transcript.search(/example.*/i) > -1,
"transcript field does not contain 'faux'");
In this case, the RegEx is in parentheses behind `search`. We are looking for the word `example`, and the other characters in the parentheses are RegEx query parameters.
`.` means that `example` must be followed by at least one character.
`*` means that any number of characters can follow `example`.
`i` means that the search is not case sensitive.
If our query tells us the word `example` was not found, and `example` `was a resource we are depending upon, this test will tell us the resource is down.
Conclusion
RegEx is difficult to get into, but extremely powerful once it's understood, because it's like a programming language inside another programming language. You can even call it as an API.
Frequently Asked Questions
What is RegEx?
RegEx is shorthand for "regular expression," which defines a pattern for searching or manipulating strings. It lets developers describe text patterns rather than fixed strings, making it useful for tasks like validation and extraction.
What does RegEx stand for?
RegEx stands for "regular expression." The term is often shortened to RegEx or simply regex in everyday developer use.
How does RegEx work?
RegEx works by combining metacharacters and quantifiers to match patterns in text. For example, a character class like [ae] matches either "a" or "e", the dot . means at least one character follows, and * means any number of characters can follow. Flags adjust behavior, such as i for case-insensitive matching, \b for word boundaries, and a global flag to check results across the whole string.
What is RegEx used for?
RegEx is used to search, validate, and manipulate strings. Common examples from the article include validating email addresses, validating domain names in URLs, removing repeated words from text, extracting HTML tags such as <title></title>, and checking API responses in JSON files.
Why does RegEx look so complicated?
RegEx can look complex at first because it acts like a programming language inside another programming language, using dense combinations of metacharacters and quantifiers. Once understood, it is extremely powerful for handling string validation and manipulation.
Can RegEx be used with an API?
Yes. The article notes that RegEx can be called as an API and can be used to validate API responses, such as checking values inside a JSON file returned by a request.
