Regular Expressions 101

Explanation

Pro

^start of string

Negative Lookahead(?!-0?(\.0+)?(e|$))

-the literal - (45₁₀ / 55₈ / 2D₁₆)

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

Group 1(\.0+)?

?repeats the group contents below at most once:

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

0+the literal 0 (48₁₀ / 60₈ / 30₁₆) , repeated at least once

Group 2(e|$)

1st Alternativee

ethe literal e (101₁₀ / 145₈ / 65₁₆) (case insensitive)

2nd Alternative$

$end of string, or before its final line terminator

-?optionally matches the literal - (45₁₀ / 55₈ / 2D₁₆)

Group 3(0|[1-9]\d*)?

?repeats the group contents below at most once:

1st Alternative0

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

2nd Alternative[1-9]\d*

Character Class[1-9]

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

\d*a Unicode decimal digit, repeated any number of times

Group 4(\.\d+)?

?repeats the group contents below at most once:

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

\d+a Unicode decimal digit, repeated at least once

Positive Lookbehind(?<=\d)

\da Unicode decimal digit

Group 5(e-?(0|[1-9]\d*))?

?repeats the group contents below at most once:

ethe literal e (101₁₀ / 145₈ / 65₁₆) (case insensitive)

-?optionally matches the literal - (45₁₀ / 55₈ / 2D₁₆)

Group 6(0|[1-9]\d*)

1st Alternative0

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

2nd Alternative[1-9]\d*

Character Class[1-9]

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

\d*a Unicode decimal digit, repeated any number of times

$end of string, or before its final line terminator

Global pattern flags

i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters

Unit Test Summary

Ready to run

Quick Reference

25 tokens

Regular Expression

^(?!-0?(\.0+)?(e|$))-?(0|[1-9]\d*)?(\.\d+)?(?<=\d)(e-?(0|[1-9]\d*))?$

Regular Expression

Unit Tests