FAQ 6.1: How can I hope to use regular expressions without creating illegible and unmainta...

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6.1: How can I hope to use regular expressions without creating illegible and
unmaintainable code?

    Three techniques can make regular expressions maintainable and

    Comments Outside the Regex
        Describe what you're doing and how you're doing it, using normal
        Perl comments.

            # turn the line into the first word, a colon, and the
            # number of characters on the rest of the line
            s/^(\w+)(.*)/ lc($1) . ":" . length($2) /meg;

    Comments Inside the Regex
        The "/x" modifier causes whitespace to be ignored in a regex pattern
        (except in a character class), and also allows you to use normal
        comments there, too. As you can imagine, whitespace and comments
        help a lot.

        "/x" lets you turn this:


        into this:

            s{ <                    # opening angle bracket
                (?:                 # Non-backreffing grouping paren
                     [^>'"] *       # 0 or more things that are neither > nor '
nor "
                        |           #    or else
                     ".*?"          # a section between double quotes (stingy
                        |           #    or else
                     '.*?'          # a section between single quotes (stingy
                ) +                 #   all occurring one or more times
               >                    # closing angle bracket
            }{}gsx;                 # replace with nothing, i.e. delete

        It's still not quite so clear as prose, but it is very useful for
        describing the meaning of each part of the pattern.

    Different Delimiters
        While we normally think of patterns as being delimited with "/"
        characters, they can be delimited by almost any character. perlre
        describes this. For example, the "s///" above uses braces as
        delimiters. Selecting another delimiter can avoid quoting the
        delimiter within the pattern:

            s/\/usr\/local/\/usr\/share/g;      # bad delimiter choice
            s#/usr/local#/usr/share#g;          # better


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