Simple "/ regex /"
Regex quick reference
[abc] A single character: a, b or c
[^abc] Any single character but a, b, or c
[a-z] Any single character in the range a-z
[a-zA-Z] Any single character in the range a-z or A-Z
^ Start of line
$ End of line
\A Start of string
\z End of string
. Any single character
\s Any whitespace character
\S Any non-whitespace character
\d Any digit
\D Any non-digit
\w Any word character (letter, number, underscore)
\W Any non-word character
\b Any word boundary character
(...) Capture everything enclosed
(a|b) a or b
a? Zero or one of a
a* Zero or more of a
a+ One or more of a
a{3} Exactly 3 of a
a{3,} 3 or more of a
a{3,6} Between 3 and 6 of a
options: i - case insensitive m make dot match newlines x ignore
whitespace in regex o perform #{...} substitutions only once
examples w/ preg_match
preg_match("/^[a-zA-Z0-9_]+$/", $string) - returns 1 if $string
contains only a-z, A-Z, 0-9, or _ for all chars, 0 if not, or
false if error occurred.
preg_match("/^[A-Za-z]+$/", $string) - returns 1 if $string
contains chars A-Za-z
preg_match("/^[\w]+$/", $string) - returns 1 if $string
contains chars [A-Za-z0-9_]+
10/26/2025 at 07:37:55pm