/ _ \
\_\(_)/_/
 _//"\\_     more on JOHLEM.net
  /   \	                 
  
0o0o0o0o0o0o0o0o0o0o0o0o0o0o0o0o0o0o0o0o0o0o0o0o0o0o0o0o0


============================
     REGULAR EXPRESSIONS     
============================

**OVERVIEW**  
Regex are patterns for string matching, searching, and replacing.

**ANCHORS**  
- `^` : Start of string (e.g., `^abc`)  
- `$` : End of string (e.g., `xyz$`)  

**QUANTIFIERS**  
- `*` : 0 or more (e.g., `ab*`)  
- `+` : 1 or more (e.g., `ab+`)  
- `?` : 0 or 1 (e.g., `ab?`)  
- `{n}` : Exactly n times (e.g., `a{3}`)  
- `{n,}` : At least n times (e.g., `a{2,}`)  
- `{n,m}` : Between n and m times (e.g., `a{2,4}`)  

**CHARACTER CLASSES**  
- `.` : Any character except newline  
- `[abc]` : Any character in set  
- `[^abc]` : Any character NOT in set  
- `[a-z]` : Range (e.g., `[0-9]` for digits)  

**SPECIAL SEQUENCES**  
- `\d` : Digit (0-9)  
- `\D` : Non-digit  
- `\w` : Word character (letters, digits, `_`)  
- `\W` : Non-word character  
- `\s` : Whitespace (space, tab, newline)  
- `\S` : Non-whitespace  

**GROUPS & REFERENCES**  
- `(abc)` : Capturing group  
- `(?:abc)` : Non-capturing group  
- `\1` : Backreference (e.g., `(a)\1` matches "aa")  

**ALTERNATION**  
- `|` : Logical OR (e.g., `cat|dog`)  

**FLAGS**  
- `i` : Case-insensitive  
- `g` : Global match  
- `m` : Multiline mode  
- `s` : Dot matches newline  

**ESCAPING**  
Escape special characters like `. * + ? ^ $ { } [ ] \ | ( )` with `\`.  
Example: Match `1+1=2` as `1\+1=2`.  

----------------------------
   COMMON USE CASES/EXAMPLES
----------------------------

- **Email Validation**:  
  `/^[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,}$/i`  

- **Phone Number Validation**:  
  `/^\+?[1-9]\d{1,14}$/`  

- **Extract All Digits**:  
  `/\d+/g`  

- **Find Words**:  
  `/\b\w+\b/g`  

- **Remove HTML Tags**:  
  `/<[^>]*>/g`  

- **Password Strength Check** (At least 8 characters, one letter, one digit):  
  `/^(?=.*[A-Za-z])(?=.*\d)[A-Za-z\d]{8,}$/`  

**TIPS**  
- Test regex with [regex101](https://regex101.com).  
- Use flags/modifiers to simplify patterns.  
- Comment complex regex with `(?x)` for clarity.

**TABLE OF COMMON FEATURES**  

| Feature        | Symbol  | Example               |
|----------------|---------|-----------------------|
| Any character  | `.`     | `a.b` → matches "acb" |
| Start of text  | `^`     | `^abc` → "abc" start  |
| End of text    | `$`     | `xyz$` → "xyz" end    |
| Optional match | `?`     | `colou?r` → "color"   |
| Word boundary  | `\b`    | `\bword\b` → "word"   |

**CONCLUSION**  
Regex is a versatile tool for text processing. Master it to boost efficiency in programming, data analysis, and more. Practice regularly to sharpen your skills!