Using Regular Expressions
Regular expressions, often abbreviated as regex or regexp, are sequences of characters that form search patterns. They are used for matching strings within text and are a powerful tool for searching, replacing, and manipulating text.
Common Use Cases
- Searching: Finding specific patterns in text.
- Replacing: Substituting parts of text with new values.
Examples
- Mask Credit Card Numbers
- Input Regex:
^\d{3,6}$ - Replacement:
*** **** **** - Example:
- Input:
"Hi, here is my card number: visa 4242-4242-4242-4242" - Output:
"Hi, here is my card number: visa **** **** **** 4242"
- Input:
- Input Regex:
- Replace an Email Address
- Regex:
\S+@\S+\.\S+or\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b - Replacement: test@test.com
- Example:
- Input:
"Contact us at example@example.com" - Output:
"Contact us at test@test.com"
- Input:
- Regex:
- Extract URLs from Text
- Regex:
https?://[^\s]+ - Matches:
http://example.comhttps://www.company.org/page
- Example:
- Input:
"Check out our website at https://www.company.com and our blog at http://blog.company.com" - Output:
["https://www.company.com", "http://blog.company.com"]
- Input:
- Regex:
- Find Phone Numbers in Various Formats
- Regex:
\b\d{3}[-.\s]??\d{3}[-.\s]??\d{4}\b|\(\d{3}\)\s*\d{3}[-.\s]??\d{4}\b - Matches:
123-456-7890(123) 456-7890123.456.7890
- Example:
- Input:
"You can reach us at 123-456-7890 or (123) 456-7890" - Output:
["123-456-7890", "(123) 456-7890"]
- Input:
- Regex:
- Extract Dates from Text
- Regex:
\b\d{1,2}[\/.-]\d{1,2}[\/.-]\d{2,4}\b - Matches:
12/31/202431-12-20242024.12.31
- Example:
- Input:
"The event is scheduled for 12/31/2024 or 31-12-2024" - Output:
["12/31/2024", "31-12-2024"]
- Input:
- Regex:
- Extract Prices from Text
- Regex:
\$\d+(?:\.\d{2})? - Matches:
$19.99$100
- Example:
- Input:
"The price of the product is $19.99 or you can buy it in bulk for $100" - Output:
["$19.99", "$100"]
- Input:
- Regex:
- Match multiple keywords
- Regex:
\b(marketing|sales|advertising|promotion)\b - Matches:
marketingsalesadvertisingpromotion
- Example:
- Input:
"Our marketing and sales teams are collaborating on the new advertising campaign" - Output:
["marketing", "sales", "advertising"]
- Input:
- Regex:
- Match a single digit
- Regex:
\d[for matching multiple digits at once like 1234 use:\d+] - Replacement: 100
- Example:
- Input:
"There are 3 apples" - Output:
"There are 100 apples"
- Input:
- Regex:
- Find All Words Starting with ‘a’
- Regex:
\ba\w* - Replacement: mango
- Matches:
- Input:
"apple" - Output:
"mango"
- Input:
- Regex:
Basic Syntax
- Literal Characters: These are the simplest form of regular expressions. For example,
catmatches the string “cat”. - Metacharacters: Special characters that have specific meanings:
.: Matches any single character except newline.- “: Matches zero or more occurrences of the preceding element.
+: Matches one or more occurrences of the preceding element.?: Matches zero or one occurrence of the preceding element.^: Matches the start of a string.$: Matches the end of a string.[]: Matches any one of the characters within the brackets.|: Acts as a logical OR between patterns.\\: Escapes a special character to be treated as a literal.
Advanced Tips
- Grouping and Capturing: Use parentheses
()to group parts of a regex and capture them for later use.- Example:
(abc)+matches one or more occurrences of the sequence “abc”.
- Example:
- Non-Capturing Groups: Use
(?:...)to group parts of a regex without capturing.- Example:
(?:abc)+matches one or more occurrences of “abc” but does not capture the group.
- Example:
- Lookahead and Lookbehind: These are assertions that match a group before or after a main pattern without including them in the result.
- Lookahead:
\\d(?=px)matches digits followed by “px” but does not include “px” in the match. - Lookbehind:
(?<=\\$)\\d+matches digits preceded by "" in the match.
- Lookahead:
Conclusion
Regular expressions are a versatile tool for text processing, offering powerful capabilities for searching, replacing, and validating text patterns. Mastering regex can greatly enhance your ability to handle and manipulate text efficiently.
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