Regular Expressions 101

Save & Share

Flavor

  • PCRE2 (PHP >=7.3)
  • PCRE (PHP <7.3)
  • ECMAScript (JavaScript)
  • Python
  • Golang
  • Java 8

Function

  • Match
  • Substitution
  • List
  • Unit Tests
"
^(?=^.{6,9}$)(?=.*\d)(?=.*[!@#$%^&]+)(?=.*[0-9])(?=.*[a-z]).*$
"
^ asserts position at start of the string
Positive Lookahead
(?=^.{6,9}$)
Assert that the Regex below matches
^ asserts position at start of the string
.
matches any character (except for line terminators)
{6,9} matches the previous token between 6 and 9 times, as many times as possible, giving back as needed (greedy)
$ asserts position at the end of the string, or before the line terminator right at the end of the string (if any)
Positive Lookahead
(?=.*\d)
Assert that the Regex below matches
.
matches any character (except for line terminators)
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
\d matches a digit (equivalent to [0-9])
Positive Lookahead
(?=.*[!@#$%^&]+)
Assert that the Regex below matches
.
matches any character (except for line terminators)
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
Match a single character present in the list below
[!@#$%^&]
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
!@#$%^&
matches a single character in the list !@#$%^& (case sensitive)
Positive Lookahead
(?=.*[0-9])
Assert that the Regex below matches
.
matches any character (except for line terminators)
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
Match a single character present in the list below
[0-9]
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
Positive Lookahead
(?=.*[a-z])
Assert that the Regex below matches
.
matches any character (except for line terminators)
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
Match a single character present in the list below
[a-z]
a-z matches a single character in the range between a (index 97) and z (index 122) (case sensitive)
.
matches any character (except for line terminators)
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
$ asserts position at the end of the string, or before the line terminator right at the end of the string (if any)
Your regular expression does not match the subject string.

Regular Expression
No Match

r"
"

Test String