Regular Expressions 101

@regex101
Donate
Sponsor
Contact
Bug Reports & Feedback
Wiki
Whats new?

Save & Share

  • Save Regex
    ctrl+s
  • Update Regex
    ctrl+⇧+s

Flavor

  • PCRE2 (PHP >=7.3)
  • PCRE (PHP <7.3)
  • ECMAScript (JavaScript)
  • Python 2.7
  • Golang
  • Java 8

Function

  • Match
  • Substitution
  • List
  • Unit Tests
/
(?<=[0-9])(?=\d$)\d
/
gm
Positive Lookbehind
(?<=[0-9])
Assert that the Regex below matches
Match a single character present in the list below
[0-9]
{12} matches the previous token exactly 12 times
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
Positive Lookahead
(?=\d$)
Assert that the Regex below matches
\d
matches a digit (equivalent to [0-9])
* 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 a line
\d matches a digit (equivalent to [0-9])
Global pattern flags
g modifier: global. All matches (don't return after first match)
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
gm

Test String

Substitution

Processing...