Do you format and comment your regular expressions?

Updated by Brady Stroud [SSW] 6 months ago. See history

123

<introEmbed body={<> Regular expressions are a very powerful tool for pattern matching, but a complicated regex can be very difficult for a human to read and to comprehend. That is why, like any good code, a good regular expression must be well formatted and documented. </>} />

Here are some guidelines when formatting and documenting your regex:

Keep each line under 80 characters, horizontal scrolling reduces readability
Break long patterns into multiple lines, usually after a space or a line break
Indent bracers to help think in the right scope
Format complicated OR patterns into multiple blocks like a case statement
Comment your regex on what it does, don't just translate it into English


# Match <BODY
<BODY
# Match any non > char for zero to infinite number of times
[^>]*
# MATCH >
>

❌ Figure: Bad example: Comment that translates the regex into English

# Match the BODY tag
<BODY
# Match any character in the body tag
[^>]*
# Match the end BODY tag
>

✅ Figure: Good example: Comment that explains the purpose of the pattern

(?six-mn:(Label|TextBox)\s+(?<Name>\w+).*(?<Result>\k<Name>\.TextAlign\s*=\s* ((System\.)?Drawing\.)?ContentAlignment\.(?! TopLeft|MiddleLeft|TopCenter|MiddleCenter)\w*)(?!(?<=\k<Name>\.Image.*)|(?
=.*\k<Name>\.Image)))

❌ Figure: Bad example: Pray you never have to modify this regex

(?six-mn:
    # Match for Label or TextBox control
    # Store name into <name> group
    (Label|TextBox)\s+(?<Name>\w+).*

    # Match any non-standard TextAlign
    # Store any match in Result group for error reporting in CA
    (?<Result>
        # Match for control's TextAlign Property
        \k<Name>\.TextAlign\s*=\s*

        # Match for possible namespace
        ((System\.)?Drawing\.)?ContentAlignment\.

        # Match any ContentAlignment that is not in the group
        (?!TopLeft|MiddleLeft|TopCenter|MiddleCenter)\w*
    )

    # Skip any Control that has image on it
    (?!
        (?<=
            \k<Name>\.Image
            .*
        )
    |
        (?=
            .*
            \k<Name>\.Image
        )
    )
)

✅ Figure: Good example: Now it make sense!

Acknowledgements

Related rules

Need help?

SSW Consulting has over 30 years of experience developing awesome software solutions.

Do you format and comment your regular expressions?

Categories

Acknowledgements

Need help?