preg_match('/\b(express\w+)\b/', $string, $matches); // matches expression
preg_match('/\b(\w*form\w*)\b/', $string, $matches); // matches perform,
// formation, unformatted
Where:
\b
is a word boundary\w+
is one or more “word” character*\w*
is zero or more “word” characters
See the manual on escape sequences for PCRE.
* Note: although not really a “word character”, the underscore _
is also included int the character class \w
.