RegEx Examples: Mastering Regular Expressions with Practical Cases

Regex, short for regular expressions, is a powerful tool used for text processing and manipulation in programming. It allows developers to define patterns of characters that can be used to match specific strings of text. This can be incredibly useful for tasks such as data validation, parsing, and searching. Regex is used in a wide range of programming languages, including Javascript, Python, and Ruby. For those looking to learn more about regex, a regex tutorial is a great place to start. A good tutorial will cover the basics of regex syntax, provide examples of common use cases, and offer best practices for working with regular expressions. By learning regex, programmers can enhance their skills and write more efficient and effective code.

What are Regular Expressions (RegEx) patterns?

A RegEx pattern is a set of rules applied to match a certain data, let's say an email address, phone number, url and a long list of etc. Everything that follows a strict pattern can be translated into a RegEx pattern.

Creating a RegEx pattern can be tricky, if you're not familiarized with Regular Expressions, so to make our lives easier, here you'll find a list of examples for most used data patterns.

RegEx for emails

Emails are one of the data we receive and have to validate, that's why we are stating our examples with an email pattern that will match any valid email inside a text.

RegEx email inside text

Javascript

1// We receive a text like this, and we want to extract the email address
2const text = `My name is Geek and my email address is geek@4geeksacademy.com`;
3
4const findEmail = (str) =>{
5  const regex = /\b[\w.!#$%&’*+\/=?^`{|}~-]+@[\w-]+(?:\.[\w-]+)*\b/mg;
6  return  str.match(regex)
7}
8
9console.log(findEmail(text))
10//Output -> [geek@4geeksacademy.com]

Python

1dataset = "My name is Geek and my mail address is geek@4geeksacademy.com";
2regex = r"\b[\w.!#$%&’*+\/=?^`{|}~-]+@[\w-]+(?:\.[\w-]+)*\b"
3
4def findEmail(term, text):
5    match = re.search(term, text)
6    return match
7
8print(findEmail(regex, dataset))
9#Output -> <re.Match object; span=(39, 61), match='geek@4geeksacademy.com'>

RegEx email

Javascript

1// Check valid email
2const text = `geek@4geeksacademy.com`;
3
4const validEmail = (str) =>{
5  const regex = new RegExp("^([a-zA-Z0-9._%-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,6})*$")
6  return  regex.test(str)
7}
8//Output: true

Since we are checking if the email address has the correct pattern, we are using the test method to receive a true/false response.

Python

1#Check valid email
2dataset = "geek@4geeksacademy.com"
3regex = r"^([a-zA-Z0-9._%-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,6})*$"
4def validEmail(term, text):
5    match = bool(re.search(term, text))
6    return match
7
8print(validEmail(regex, dataset))
9#Output -> True

Since we are checking if the email address has the correct pattern, we are using the bool to receive a true/false response.

Numbers without decimals (Int)

Javascript

1//Check integer
2const text = `15 
312.3 
456,7 
512/4`;
6
7const checkInt = (str) =>{
8  const regex = /^(\d+)$/gm;
9  return  str.match(regex)
10}
11
12console.log(checkInt(text))
13//Output -> [15]

Python

1#Check integer
2number = ("15\n"
3	"12.3\n"
4	"56,7\n"
5	"12/4")
6regex = r"^(\d+)$"
7def checkInt(term, text):
8    dataset = "".join(text)
9    match= re.search(term, dataset, re.MULTILINE)
10    return match
11
12print(checkInt(regex, number))
13#output -> <re.Match object; span=(0, 2), match='15'>

RegEx decimal numbers (float)

Javascript

1#Check float
2const text = `15 
312.3 
456,7 
512/4`;
6
7const checkFloat = (str) =>{
8  const regex = /^(\d*)[.,](\d+)$/gm;
9  return  str.match(regex)
10}
11
12console.log(checkFloat(text))
13//Output -> [ '12.3', '56,7' ]

Python

1#Check Float
2number = ("15\n"
3	"12.3\n"
4	"56,7\n"
5	"12/4")
6regexFloat = r"^(\d*)[.,](\d+)$"
7def checkInt(term, text):
8    dataset = "".join(text)
9    match= re.findall(term, dataset, re.MULTILINE)
10    return match
11
12print(checkInt(regexFloat, number))
13#output -> [('12', '3'), ('56', '7')]

We are using the findall() method because we have more than one in our dataset, if you would only want one result, use the search() method instead. The output would be <re.Match object; span=(3, 7), match='12.3'>

Regex for decimals

Javascript

1const text = `15 
212.3 
356,7 
412/4`;
5
6const checkDecimals = (str) =>{
7  const regex = /^(\d+)[\/](\d+)$/gm;
8  return  str.match(regex)
9}
10
11console.log(checkDecimals(text))
12//Output -> [ '12/4' ]

Python

1#Check decimals
2number = ("15\n"
3	"12.3\n"
4	"56,7\n"
5	"12/4")
6
7regexDecimals = r"^(\d+)[\/](\d+)$"
8def checkDecimals(term, text):
9    dataset = "".join(text)
10    match= re.search(term, dataset, re.MULTILINE)
11    return match
12
13print(checkDecimals(regexDecimals, number))
14#Output -> <re.Match object; span=(13, 17), match='12/4'>

RegEx for strong password validation

A strong password consists on a minimum length of 6 characters and at least:

• 1 uppercase
• 1 lowercase
• 1 number
• 1 special character

Javascript

1#Check password
2const goodPass = `%G[e](e)?k@1&3$`
3const badPass = `
4geek@123 
5GEEK@123 
6Geeks123 
7Geeks@Geeks`
8
9const checkPass = (pass) =>{
10const regex = /(?=^.{6,}$)((?=.*\w)(?=.*[A-Z])(?=.*[a-z])(?=.*[0-9])(?=.*[|!@\[\]\(\)?$%&\/\(\)\?\^\'\\\+\-\*]))^.*/gm;
11  return regex.test(pass)
12}
13console.log(checkPass(goodPass)) //Output -> true
14console.log(checkPass(badPass)) //Output -> false

Python

1goodPass = "%G[e](e)?k@1&3$"
2badPass = ("geek@123\n" 
3"GEEK@123\n"
4"Geeks123\n"
5"Geeks@Geeks")
6regex = r"(?=^.{6,}$)((?=.*\w)(?=.*[A-Z])(?=.*[a-z])(?=.*[0-9])(?=.*[|!\"$%&\/\(\)\?\^\'\\\+\-\*]))^.*"
7def checkPassword(term, text):
8    match = bool(re.search(term, text, re.MULTILINE))
9    return match
10
11print(checkPassword(regex, goodPass)) #Output -> True
12print(checkPassword(regex, badPass)) #Output -> False

In both cases, we are returning True/False if the password provided matches the requirements.

RegEx for URLs

Javascript

1// Check url
2const checkUrl = (url) =>{
3	const regex = /^(((https?|ftp):\/\/)?([\w\-\.])+(\.)([\w]){2,4}([\w\/+=%&_\.~?\-]*))*$/gm;
4 	return regex.test(url)
5	}
6
7console.log(checkUrl("www.4geeks.com")) //Output -> true
8console.log(checkUrl("4geeks.com")) //Output -> true
9console.log(checkUrl("http://www.google.com")) //Output -> true
10console.log(checkUrl("4geeks")) //Output -> false

Python

1#check url
2def checkUrl(url):
3    regex = r"^(((https?|ftp):\/\/)?([\w\-\.])+(\.)([\w]){2,4}([\w\/+=%&_\.~?\-]*))*$"
4    match= bool(re.search(regex, url))
5    return match
6
7print(checkUrl("www.4geeks.com")) #Output -> True
8print(checkUrl("4geeks.com")) #Output -> True
9print(checkUrl("http://www.google.com")) #Output -> True
10print(checkUrl("4geeks")) #Output -> False

In both cases we are returning a boolean (true/false) if the URL is valid.

You can learn more about this topic and others related at 4Geeks. Hope you enjoyed the reading and keep on the Geek side!