Regular Expressions 101

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/
^\(\d{3}\)\s?\d{3}\-\d{4}$
/
m
^ asserts position at start of a line
\( matches the character ( with index 4010 (2816 or 508) literally (case sensitive)
\d
matches a digit (equivalent to [0-9])
{3} matches the previous token exactly 3 times
\) matches the character ) with index 4110 (2916 or 518) literally (case sensitive)
\s
matches any whitespace character (equivalent to [\r\n\t\f\v \u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff])
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\d
matches a digit (equivalent to [0-9])
{3} matches the previous token exactly 3 times
\- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
\d
matches a digit (equivalent to [0-9])
{4} matches the previous token exactly 4 times
$ asserts position at the end of a line
Global pattern flags
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.

Regular Expression
No Match

/
/
m

Test String