vitorbritto · September 27, 2025 02:41 · Jun 17, 2020 · Jun 9, 2014 · Jun 9, 2014
diff --git a/regex.md b/regex.md
@@ -63,7 +63,7 @@
 - `*`: 0 or more
 - `+`: 1 or more
 - `?`: 0 or 1
-- `{3`: Exactly 3
+- `{3}`: Exactly 3
 - `{3,}`: 3 or more
 - `{3,5}`: 3, 4 or 5
 

diff --git a/regex.md b/regex.md
@@ -1,10 +1,9 @@
-
 # Regular Expressions
 
 
 ## Basic Syntax
 
-- `/.../`: Start and end regex delimiters |
+- `/.../`: Start and end regex delimiters
 - `|`: Alternation
 - `()`: Grouping
 

diff --git a/regex.md b/regex.md
@@ -0,0 +1,131 @@
+
+# Regular Expressions
+
+
+## Basic Syntax
+
+- `/.../`: Start and end regex delimiters |
+- `|`: Alternation
+- `()`: Grouping
+
+
+## Position Matching
+
+- `^`: Start of string or start of line in multi-line mode
+- `\A`: Start of string
+- `$`: End of string or end of line in multi-line mode
+- `\Z`: End of string
+- `\b`: Word boundary
+- `\B`: Not word boundary
+- `\<`: Start of word
+- `\>`: End of word
+
+
+## Character Classes
+
+- `\s`: Whitespace
+- `\S`: Not whitespace
+- `\w`: Word
+- `\W`: Not word
+- `\d`: Digit
+- `\D`: Not digit
+- `\x`: Hexadecimal digit
+- `\O`: Octal digit
+
+
+## Special Characters
+
+- `\n`: Newline
+- `\r`: Carriage return
+- `\t`: Tab
+- `\v`: Vertical tab
+- `\f`: Form feed
+- `\xxx`: Octal character xxx
+- `\xhh`: Hex character hh
+
+
+## Groups and Ranges
+
+- `.`: Any character except newline (\n)
+- `(a|b)`: a or b
+- `(…)`: Group
+- `(?:…)`: Passive (non-capturing) group
+- `[abc]`: a, b or c
+- `[^abc]`: Not a, b or c
+- `[a-z]`: Letters from a to z
+- `[A-Z]`: Uppercase letters from A to Z
+- `[0-9]`: Digits from 0 to 9
+
+> Note: Ranges are inclusive.
+
+
+## Quantifiers
+
+- `*`: 0 or more
+- `+`: 1 or more
+- `?`: 0 or 1
+- `{3`: Exactly 3
+- `{3,}`: 3 or more
+- `{3,5}`: 3, 4 or 5
+
+> Note: Quantifiers are greedy - they match as many times as possible. Add a ? after the quantifier to make it ungreedy.
+
+
+## Escape Sequences
+
+- `\`:Escape following character. Used to escape any of the following metacharacters: {}[]()^$.|*+?\.
+- `\Q`: Begin literal sequence
+- `\E`: End literal sequence
+
+
+## String Replacement
+
+- `$1`: 1st group
+- `$2`: 2nd group
+- `$n`: nth group
+- `$``: Before matched string
+- `$'`: After matched string
+- `$+`: Last matched string
+- `$&`: Entire matched string
+
+> Note: Some regex implementations use \ instead of $.
+
+
+## Assertions
+
+- `?=`: Lookahead assertion
+- `?!`: Negative lookahead
+- `?<=`: Lookbehind assertion
+- ``?!=, ?<!``: Negative lookbehind
+- `?>`: Once-only subexpression
+- `?()`: Condition if-then
+- `?()|`: Condition if-then-else
+- `?#`: Comment
+
+
+## POSIX
+
+- `[:upper:]`: Uppercase letters
+- `[:lower:]`: Lowercase letters
+- `[:alpha:]`: All letters
+- `[:alnum:]`: Digits and letters
+- `[:digit:]`: Digits
+- `[:xdigit:]`: Hexadecimal digits
+- `[:punct:]`: Punctuation
+- `[:blank:]`: Space and tab
+- `[:space:]`: Blank characters
+- `[:cntrl:]`: Control characters
+- `[:graph:]`: Printed characters
+- `[:print:]`: Printed characters and spaces
+- `[:word:]`: Digits, letters and underscore
+
+
+## Pattern Modifiers
+
+- `g`: Global match
+- `i`: Case-insensitive
+- `m`: Multi-line mode. Causes ^ and $ to also match the start/end of lines.
+- `s`: Single-line mode. Causes . to match all, including line breaks.
+- `x`: Allow comments and whitespace in pattern
+- `e`: Evaluate replacement
+- `U`: Ungreedy mode