Regular Expressions 101

^start of line

Non-Capturing Group(?:(?=\d{7,9}$)[01]?|\d*(?=\d{7}$)|)

1st Alternative(?=\d{7,9}$)[01]?

Positive Lookahead(?=\d{7,9}$)

\d{7,9}a digit, repeated between 7 and 9 times

$end of line

Character Class[01]?

?matches at most one character from the set below:

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

2nd Alternative\d*(?=\d{7}$)

\d*a digit, repeated any number of times

Positive Lookahead(?=\d{7}$)

\d{7}a digit, repeated exactly 7 times

$end of line

3rd Alternative — matches an empty string

Group 1(\d+$)

\d+a digit, repeated at least once

$end of line

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

Detailed match information will be displayed here automatically.

25 tokens

Regular Expression

^(?:(?=\d{7,9}$)[01]?|\d*(?=\d{7}$)|)(\d+$)

New

555123
1234567
5551212
5551234567
12345
1234
123
12
1
012345678
1234567
0123456789
12345678900123124

555123
1234567
5551212
5551234567
12345
1234
123
12
1
012345678
1234567
0123456789
12345678900123124