Using Regular Expressions

​

Common Use Cases

• Searching: Finding specific patterns in text.
• Replacing: Substituting parts of text with new values.

​

Examples

1. 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"
2. 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"
3. Extract URLs from Text
   • Regex: https?://[^\s]+
   • Matches:
     • http://example.com
     • https://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"]
4. 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) 456-7890
     • 123.456.7890
   • Example:
     • Input: "You can reach us at 123-456-7890 or (123) 456-7890"
     • Output: ["123-456-7890", "(123) 456-7890"]
5. Extract Dates from Text
   • Regex: \b\d{1,2}[\/.-]\d{1,2}[\/.-]\d{2,4}\b
   • Matches:
     • 12/31/2024
     • 31-12-2024
     • 2024.12.31
   • Example:
     • Input: "The event is scheduled for 12/31/2024 or 31-12-2024"
     • Output: ["12/31/2024", "31-12-2024"]
6. 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"]
7. Match multiple keywords
   • Regex: \b(marketing|sales|advertising|promotion)\b
   • Matches:
     • marketing
     • sales
     • advertising
     • promotion
   • Example:
     • Input: "Our marketing and sales teams are collaborating on the new advertising campaign"
     • Output: ["marketing", "sales", "advertising"]
8. 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"
9. Find All Words Starting with ‘a’
   • Regex: \ba\w*
   • Replacement: mango
   • Matches:
     • Input: "apple"
     • Output: "mango"

​

Basic Syntax

• Literal Characters: These are the simplest form of regular expressions. For example, cat matches 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”.
• 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.
• 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 "$" but does not include "$" in the match.

​

Conclusion