Regular Expressions 101

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/
^1?[-. ]*([0-9]{3}){1}[-. ]*([0-9]{3}){1}?[-. ]*([0-9]{4}){1}$
/
gm
^ asserts position at start of a line
1
matches the character 1 with index 4910 (3116 or 618) literally (case sensitive)
Match a single character present in the list below
[-. ]
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
-.
matches a single character in the list -. (case sensitive)
1st Capturing Group
([0-9]{3}){1}
{1} matches the previous token exactly one time (meaningless quantifier)
A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data
Match a single character present in the list below
[0-9]
{3} matches the previous token exactly 3 times
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
Match a single character present in the list below
[-. ]
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
-.
matches a single character in the list -. (case sensitive)
2nd Capturing Group
([0-9]{3}){1}?
{1}? matches the previous token exactly one time (meaningless quantifier)
A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data
Match a single character present in the list below
[0-9]
{3} matches the previous token exactly 3 times
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
Match a single character present in the list below
[-. ]
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
-.
matches a single character in the list -. (case sensitive)
3rd Capturing Group
([0-9]{4}){1}
{1} matches the previous token exactly one time (meaningless quantifier)
A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data
Match a single character present in the list below
[0-9]
{4} matches the previous token exactly 4 times
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
$ 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