Regular Expressions 101

Pro

^start of line

Negative Lookahead(?!.*(?<!\S)opt3(?!\S))

.*any Unicode character (except for line terminators), repeated any number of times

Negative Lookbehind(?<!\S)

\Sany character that is not Unicode whitespace

opt3the literal text opt3 (case sensitive)

Negative Lookahead(?!\S)

\Sany character that is not Unicode whitespace

filenamethe literal text filename (case sensitive)

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

txtthe literal text txt (case sensitive)

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

^(?!.*(?<!\S)opt3(?!\S))filename\.txt

New

filename.txt  opt1 opt2 opt4 testopt3test
filename.txt  opt1 opt2 opt4 $opt3#
filename.txt  opt1 opt2 opt4 opt3