Regular Expressions 101

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/
^(?!.*\bjack\b.*\bjack\b)(?!.*\bjames\b.*\bjames\b)(?=.*\bjames\b)(?=.*\bjack\b).*$
/
gm
^ asserts position at start of a line
Negative Lookahead
(?!.*\bjack\b.*\bjack\b)
Assert that the Regex below does not match
.
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)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
jack
matches the characters jack literally (case sensitive)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
.
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)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
jack
matches the characters jack literally (case sensitive)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
Negative Lookahead
(?!.*\bjames\b.*\bjames\b)
Assert that the Regex below does not match
.
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)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
james
matches the characters james literally (case sensitive)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
.
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)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
james
matches the characters james literally (case sensitive)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
Positive Lookahead
(?=.*\bjames\b)
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)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
james
matches the characters james literally (case sensitive)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
Positive Lookahead
(?=.*\bjack\b)
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)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
jack
matches the characters jack literally (case sensitive)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
.
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 a line
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

Code Generator

Generated Code

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Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report.
For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php