Regular Expressions 101

Explanation

Pro

Group 1(\d+)?

?repeats the group contents below at most once:

\d+a digit, repeated at least once

Condition(?(1) )

Uses the first branch if group 1 matched

If the condition is true, match this branch:

the literal (32₁₀ / 40₈ / 20₁₆)

Group 2(foo)

foothe literal text foo (case sensitive)

Condition(?(1)| (\d+)(?!\d* foo))

Uses the first branch if group 1 matched

If the condition is true, match this branch: — matches an empty string

Otherwise, match this branch: (\d+)(?!\d* foo)

the literal (32₁₀ / 40₈ / 20₁₆)

Group 3(\d+)

\d+a digit, repeated at least once

Negative Lookahead(?!\d* foo)

\d*a digit, repeated any number of times

foothe literal text foo (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

(\d+)?(?(1) )(foo)(?(1)| (\d+)(?!\d* foo))

New

1234 foo
foo 1234extra_word_chars
1234 foo 1234
foo 1234 foo

1234 foo
foo 1234extra_word_chars
1234 foo 1234
foo 1234 foo