Regular Expressions 101

1st Alternative \b # "word" boundary (?<=\$) # Assert that current position is preceded by $ \d+\b # digits, boundary (?!\$) # Assert that current position is not followed by $

\ban ASCII word boundary

Comment: "word" boundary

Positive Lookbehind(?<=\$)

\$the literal $ (36₁₀ / 44₈ / 24₁₆)

Comment: Assert that current position is preceded by $

\d+a digit, repeated at least once

\ban ASCII word boundary

Comment: digits, boundary

Negative Lookahead(?!\$)

\$the literal $ (36₁₀ / 44₈ / 24₁₆)

Comment: Assert that current position is not followed by $

2nd Alternative # alternation \b # boundary (?<!\$) # Assert that current position not preceded by $ \d+\b # digits, boundary (?=\$) # Assert that current position is followed by $

Comment: alternation

\ban ASCII word boundary

Comment: boundary

Negative Lookbehind(?<!\$)

\$the literal $ (36₁₀ / 44₈ / 24₁₆)

Comment: Assert that current position not preceded by $

\d+a digit, repeated at least once

\ban ASCII word boundary

Comment: digits, boundary

Positive Lookahead(?=\$)

\$the literal $ (36₁₀ / 44₈ / 24₁₆)

Comment: Assert that current position is followed by $

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

x modifier: extended. Ignores unescaped whitespace and comments outside character classes

Detailed match information will be displayed here automatically.

Search reference

Regular Expression

  \b       # "word" boundary
  (?<=\$)  # Assert that current position is preceded by $
  \d+\b    # digits, boundary
  (?!\$)   # Assert that current position is not followed by $
|          # alternation
  \b       # boundary
  (?<!\$)  # Assert that current position not preceded by $
  \d+\b    # digits, boundary
  (?=\$)   # Assert that current position is followed by $

Test String
New

$15
16$
$17$
18

Regular Expression

Test StringNew

Test String
New