Regular Expressions 101

Pro

^start of line

Group 1(((.)(?=. \3))?(?=[0-8]?(\d? \d?)[1-9])(?=0?\4[1]|1\4?2|2\4?3|3\4?4|4\4?5|5\4?6|6\4?7|7\4?8|8\4?9|9\4?0).?9? ){98}

{98}repeats the group contents below exactly 98 times:

Group 2((.)(?=. \3))?

?repeats the group contents below at most once:

Group 3(.)

.any character (except for line terminators)

Positive Lookahead(?=. \3)

.any character (except for line terminators)

the literal (32₁₀ / 40₈ / 20₁₆)

\3the text saved by group 3

Positive Lookahead(?=[0-8]?(\d? \d?)[1-9])

Character Class[0-8]?

?matches at most one character from the set below:

0-8one character from 0 (48₁₀) to 8 (56₁₀)

Group 4(\d? \d?)

\d?optionally matches a digit

the literal (32₁₀ / 40₈ / 20₁₆)

\d?optionally matches a digit

Character Class[1-9]

1-9one character from 1 (49₁₀) to 9 (57₁₀)

Positive Lookahead(?=0?\4[1]|1\4?2|2\4?3|3\4?4|4\4?5|5\4?6|6\4?7|7\4?8|8\4?9|9\4?0)

1st Alternative0?\4[1]

0?optionally matches the literal 0 (48₁₀ / 60₈ / 30₁₆)

\4the text saved by group 4

Character Class[1]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

2nd Alternative1\4?2

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

\4?optionally matches the text saved by group 4

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

3rd Alternative2\4?3

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

\4?optionally matches the text saved by group 4

3the literal 3 (51₁₀ / 63₈ / 33₁₆)

4th Alternative3\4?4

3the literal 3 (51₁₀ / 63₈ / 33₁₆)

\4?optionally matches the text saved by group 4

4the literal 4 (52₁₀ / 64₈ / 34₁₆)

5th Alternative4\4?5

4the literal 4 (52₁₀ / 64₈ / 34₁₆)

\4?optionally matches the text saved by group 4

5the literal 5 (53₁₀ / 65₈ / 35₁₆)

6th Alternative5\4?6

5the literal 5 (53₁₀ / 65₈ / 35₁₆)

\4?optionally matches the text saved by group 4

6the literal 6 (54₁₀ / 66₈ / 36₁₆)

7th Alternative6\4?7

6the literal 6 (54₁₀ / 66₈ / 36₁₆)

\4?optionally matches the text saved by group 4

7the literal 7 (55₁₀ / 67₈ / 37₁₆)

8th Alternative7\4?8

7the literal 7 (55₁₀ / 67₈ / 37₁₆)

\4?optionally matches the text saved by group 4

8the literal 8 (56₁₀ / 70₈ / 38₁₆)

9th Alternative8\4?9

8the literal 8 (56₁₀ / 70₈ / 38₁₆)

\4?optionally matches the text saved by group 4

9the literal 9 (57₁₀ / 71₈ / 39₁₆)

10th Alternative9\4?0

9the literal 9 (57₁₀ / 71₈ / 39₁₆)

\4?optionally matches the text saved by group 4

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

.?optionally matches any character (except for line terminators)

9?optionally matches the literal 9 (57₁₀ / 71₈ / 39₁₆)

the literal (32₁₀ / 40₈ / 20₁₆)

99 100the literal text 99 100

$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

x

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25 tokens

Regular Expression

^(((.)(?=. \3))?(?=[0-8]?(\d? \d?)[1-9])(?=0?\4[1]|1\4?2|2\4?3|3\4?4|4\4?5|5\4?6|6\4?7|7\4?8|8\4?9|9\4?0).?9? ){98}99 100$

Unit Tests

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