 | RegEx > Programming RegEx (Javascript, PHP, ...) |  |
Regular Expressions are great! You can use the in lots of editors like `notepad++' or `visual studio' - there are even a whole range of online tools, like https://regexr.com/. However, there will be times when you'll want to use regular expression with your own languages and tools. Of course, they're supported by everyone and everywhere.
Let's take a look at a few popular languages like 'Python', 'Javascript' and 'PHP' and how you'd go about using regular expressions - not just for `finding' but also for replacing and inserting.
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Using Regular Expressions in JavaScript |
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Creating a Regular Expression
| Method |
Example |
| RegExp Constructor |
let regex = new RegExp("pattern"); |
| Literal Notation |
let regex = /pattern/; |
Basic Methods
| Method |
Example |
test() |
let result = regex.test(str); |
exec() |
let result = regex.exec(str); |
String Methods
| Method |
Example |
match() |
let result = str.match(regex); |
replace() |
let newStr = str.replace(regex, "replacement"); |
split() |
let result = str.split(regex); |
Flags
| Flag |
Description |
Example |
i |
Case-insensitive matching |
/pattern/i |
g |
Global matching |
/pattern/g |
m |
Multiline matching |
/pattern/m |
Example
let pattern = /apple/gi;
let str = "Apple is a fruit. I love eating apples!";
let result = str.match(pattern); // ["Apple", "apples"]
Regular expressions in JavaScript are a powerful tool for pattern matching and manipulation in strings. This overview covers the basics, and you can explore more advanced features as you become more familiar with regex.
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Using Regular Expressions in Python |
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Importing the `re` Module
| Method |
Example |
| Import |
import re |
Creating a Regular Expression
| Method |
Example |
| Compile |
pattern = re.compile(r'your_pattern_here') |
Basic Methods
| Method |
Example |
search() |
match = pattern.search(text) |
match() |
match = pattern.match(text) |
findall() |
matches = pattern.findall(text) |
Other Methods
| Method |
Example |
finditer() |
matches = pattern.finditer(text) |
sub() |
new_text = pattern.sub("replacement", text) |
split() |
words = pattern.split(text) |
Flags
| Flag |
Description |
Example |
re.IGNORECASE |
Case-insensitive matching |
pattern = re.compile(r'pattern', re.IGNORECASE) |
Examples
import re
pattern = re.compile(r'\b\w{3}\b')
text = "The cat is on the mat."
matches = pattern.findall(text)
print("Three-letter words:", matches)
Regular expressions in Python are versatile and can be applied to a wide range of tasks involving text processing. The re module documentation provides more details and options for advanced usage.
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Using Regular Expressions in PHP |
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1. Using preg_match() for Simple Pattern Matching
| Function |
Example |
preg_match() |
$pattern = '/apple/';
$text = 'I like apples and oranges.';
if (preg_match($pattern, $text)) {
echo 'Pattern found!';
} else {
echo 'Pattern not found.';
}
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2. Using preg_match_all() to Find All Matches
| Function |
Example |
preg_match_all() |
$pattern = '/\d+/';
$text = 'There are 42 apples and 7 oranges.';
if (preg_match_all($pattern, $text, $matches)) {
print_r($matches[0]); // Array containing all matches
} else {
echo 'No matches found.';
}
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3. Using preg_replace() for Pattern Replacement
| Function |
Example |
preg_replace() |
$pattern = '/apple/';
$text = 'I have an apple.';
$replacement = 'orange';
$newText = preg_replace($pattern, $replacement, $text);
echo $newText; // Output: "I have an orange."
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4. Using preg_split() for String Splitting
| Function |
Example |
preg_split() |
$pattern = '/\s+/';
$text = 'This is a sentence.';
$words = preg_split($pattern, $text);
print_r($words); // Array containing individual words
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5. Using Regular Expression Flags
| Function |
Example |
| Flags |
$pattern = '/apple/i'; // Case-insensitive matching
$text = 'I like Apples and Oranges.';
if (preg_match($pattern, $text)) {
echo 'Pattern found!';
} else {
echo 'Pattern not found.';
}
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6. Using Capture Groups
| Function |
Example |
preg_match() with Capture Groups |
$pattern = '/(\d{2})-(\d{2})-(\d{4})/';
$text = 'Date of birth: 12-31-2000';
if (preg_match($pattern, $text, $matches)) {
echo 'Day: ' . $matches[1] . ', Month: ' . $matches[2] . ', Year: ' . $matches[3];
} else {
echo 'Pattern not found.';
}
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7. Escaping Special Characters
| Function |
Example |
preg_quote() |
$pattern = '/[.*+?^${}()|\[\]\]/';
$escapedPattern = preg_quote('[.*+?^${}()|[\]', '/');
echo $escapedPattern; // Output: \[\.\*\+\?\^$\{\}\(\)\|\[\\]
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These examples cover the basics of using regular expressions in PHP.
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