Regular Expressions 101

Explanation
Pro

^start of line

Positive Lookahead(?=.+)

.+any character (except for line terminators), repeated at least once

Non-Capturing Group(?:[1-9]\d*|0)?

?repeats the group contents below at most once:

1st Alternative[1-9]\d*

Character Class[1-9]

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

\d*a digit, repeated any number of times

2nd Alternative0

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

Non-Capturing Group(?:\.\d+)?

?repeats the group contents below at most once:

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

\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

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

New

123456
123.
.
.123
123.154574
.545.4584
+1454
+487.54587
-54587.7487
.1225-
.456+
454.4+
454.455874
45.45745687687.5678

123456
123.
.
.123
123.154574
.545.4584
+1454
+487.54587
-54587.7487
.1225-
.456+
454.4+
454.455874
45.45745687687.5678