Regular Expressions 101

Explanation

Pro

^start of line

Negative Lookahead(?!\s)

\sany whitespace character

.{0,20}any character (except for line terminators), repeated between 0 and 20 times

Negative Lookbehind(?<!\s)

\sany whitespace character

$end of line

Global pattern flags

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

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

Detailed match information will be displayed here automatically.

25 tokens

^(?!\s).{0,20}(?<!\s)$

New

123456789012345678901234567890
123456789012345678
123456789012345678901
 1234567890
1234567890 
 1234567890