Answers for "regular expression cheatsheet"

regular expression cheatsheet

Regular Expression FUll Cheatsheet (For quick look) :)
note: for downloading visit https://buggyprogrammer.com/regular-expression-cheatsheet/
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# -------------- Anchors --------------
^   →  Start of string, or start of line in multiline pattern
\A  →  Start of string
$   →  End of string, or end of line in multi-line pattern
\Z  →  End of string
\b  →  Word boundary
\B  →  Not word boundary
\<  →  Start of word
\>  →  End of word


# ---------- Character Classes --------
\c  →  Control character
\s  →  White space
\S  →  Not white space
\d  →  Digit
\D  →  Not digit
\w  →  Word
\W  →  Not word
\x  →  Hexadecimal digit
\O  →  Octal digit


# --------- Quantifiers -----------------
*     →    0 or more 
{3}   →    Exactly 3
+     →    1 or more 
{3,}  →    3 or more
?     →    0 or 1 
{3,5} →    3, 4 or 5
Add a ? to a quantifier to make it ungreedy.


# ------- Special Characters -------------
\n   →  New line
\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 new line (\n)
(a|b)   →  a or b
(...)   →  Group
(?:...) →  Passive (non-capturing) group
[abc]   →  Range (a or b or c)
[^abc]  →  Not (a or b or c)
[a-q]   →  Lower case letter from a to q
[A-Q]   →  Upper case letter from A to Q
[0-7]   →  Digit from 0 to 7
\x      →  Group/subpattern number "x"
Ranges are inclusive.


# ----------- Assertions ---------------
?=         →  Lookahead assertion
?!         →  Negative lookahead
?<=        →  Lookbehind assertion
?!= or ?<! →  Negative lookbehind
?>         →  Once-only Subexpression
?()        →  Condition [if then]
?()|       →  Condition [if then else]
?#         →  Comment


# ------ Pattern Modifiers --------
g   →  Global match
i*  →  Case-insensitive
m*  →  Multiple lines
s*  →  Treat string as single line
x*  →  Allow comments and whitespace in pattern
e*  →  Evaluate replacement
U*  →  Ungreedy pattern
*   →  PCRE modifier


# ------ String Replacement ------
$n  →  nth non-passive group
$2  →  "xyz" in /^(abc(xyz))$/
$1  →  "xyz" in /^(?:abc)(xyz)$/
$`  →  Before matched string
$'  →  After matched string
$+  →  Last matched string
$&  →  Entire matched string
Some regex implementations use \ instead of $


# ---------- Escape Sequences ------------
\ Escape following character
\Q Begin literal sequence
\E End literal sequence

"Escaping" is a way of treating characters which have a special meaning in regular
expressions literally, rather than as special characters.


# --------- Common Metacharacters ---------
^ 
[
.
$
{
*
(
\
+
)
|
<
>
The escape character is usually \


# ------------ POSIX ----------------
[:upper:]  →  Upper case letters
[:lower:]  →  Lower case 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

regular expression characters

/* shorthand character classes */
regex = /d/; // matches any digit, short for [0-9]
regex = /D/; // matches non-digits, short for [^0-9]
regex = /S/; // matches non-white space character
regex = /s/; // matches any white space character
regex = /w/; // matches character, short for [a-zA-Z_0-9]
regex = /W/; // matches non-word character [^w]
regex = /b/; // Matches a word boundary where a word character is [a-zA-Z0-9_]