Regular Expression Study Link
Regular Expression in PHP with Examples
. = matches anything that has a single character
Ex: /./ matches anything that has a single character
^ = matches the beginning of string/excludes characters.
Ex. /^PH/ matches any string that starts with PH
$= matches pattern at the end of the string
/com$/ matches google.com facebook.com etc
*= matches any zero(0) or more characters
/com*/ matches computer, communication etc.
+ = requires preceding character(s) appear at least one.
\ = used to escape meta characters
Ex: /yahoo.com/ treats the dot as a literal value.
| = alternate word search
a-z = means lowercase letters
Ex: /a-z/ matches cool, happy etc
A-Z = matches uppercase letters
/A-Z/ matches WHAT, WHY etc.
0-9 = matches number between 0 and 9
Ex: /0-4/ matches 0,1,2,3,4
. any character except newline
\w\d\s word, digit, whitespace
\W\D\S not word, digit, whitespace
[a-g] character between a & g
^abc$ start / end of the string
\b\B word, not-word boundary
.*\ escaped special characters
\t\n\r tab, linefeed, carriage return
\1 backreference to group #1
(?:abc) non-capturing group
(?=abc) positive lookahead
(?!abc) negative lookahead
Quantifiers & Alternation
a*a+a? 0 or more, 1 or more, 0 or 1
a{5}a{2,} exactly five, two or more
a{1,3} between one & three
a+?a{2,}? match as few as possible
preg_match = Returns 1 if the pattern was found in the string 0 if not.
preg_replace = Returns a new string where matched pattern have been replaced with another string