Regular Expressions 101

Explanation

Pro

Negative Lookbehind(?<!\\)

\\the literal \ (92₁₀ / 134₈ / 5C₁₆)

Comment: Check it was not escaped with a \

Group bold_all(?<bold_all> (?<bold_type>\*{2}|\_{2}) # Emphasis type: * or _ (?= # followed by non-space (?: (?:[_*`\$\\]) # avoid punctuation except those | (?![[:punct:]]) ) \S) (?<bold_text>.+?[*_]*) # enclosed text (?<=\S) # making sure preceding stuff was a non-space \g{bold_type} # Balanced closing tag )

Group bold_type(?<bold_type>\*{2}|\_{2})

1st Alternative\*{2}

\*{2}the literal * (42₁₀ / 52₈ / 2A₁₆) , repeated exactly 2 times

2nd Alternative\_{2}

\_{2}the literal _ (95₁₀ / 137₈ / 5F₁₆) , repeated exactly 2 times

Comment: Emphasis type: * or _

Positive Lookahead(?= # followed by non-space (?: (?:[_*`\$\\]) # avoid punctuation except those | (?![[:punct:]]) ) \S)

Comment: followed by non-space

Non-Capturing Group(?: (?:[_*`\$\\]) # avoid punctuation except those | (?![[:punct:]]) )

1st Alternative (?:[_*`\$\\]) # avoid punctuation except those

Non-Capturing Group(?:[_*`\$\\])

Character Class[_*`\$\\]

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

*the literal * (42₁₀ / 52₈ / 2A₁₆)

`the literal ` (96₁₀ / 140₈ / 60₁₆)

\$the literal $ (36₁₀ / 44₈ / 24₁₆)

\\the literal \ (92₁₀ / 134₈ / 5C₁₆)

Comment: avoid punctuation except those

2nd Alternative (?![[:punct:]])

Negative Lookahead(?![[:punct:]])

Character Class[[:punct:]]

[:punct:]a punctuation character [!"#$%&'()*+,\-./:;<=>?@[\]^_`{|}~]

\Sany non-whitespace character

Group bold_text(?<bold_text>.+?[*_]*)

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

Character Class[*_]*

*matches any number of characters from the set below:

*the literal * (42₁₀ / 52₈ / 2A₁₆)

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

Comment: enclosed text

Positive Lookbehind(?<=\S)

\Sany non-whitespace character

Comment: making sure preceding stuff was a non-space

\g{bold_type}the text saved by group bold_type

Comment: Balanced closing tag

Global pattern flags

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

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

Unit Test Summary

Ready to run

Quick Reference

25 tokens

Regular Expression

(?<!\\)                         # Check it was not escaped with a \
(?<bold_all>
    (?<bold_type>\*{2}|\_{2})   # Emphasis type: * or _
    (?=                         # followed by non-space
        (?:
            (?:[_*`\$\\])       # avoid punctuation except those
            |
            (?![[:punct:]])
        )
    \S)
    (?<bold_text>.+?[*_]*)      # enclosed text
    (?<=\S)                     # making sure preceding stuff was a non-space
    \g{bold_type}               # Balanced closing tag
)

Regular Expression

Unit Tests