Beefy Boxes and Bandwidth Generously Provided by pair Networks
P is for Practical

How do I write a regex which allows meta-quoting?

by WHolcomb (Initiate)
on Apr 13, 2000 at 19:03 UTC ( #7467=categorized question: print w/replies, xml ) Need Help??
Contributed by WHolcomb on Apr 13, 2000 at 19:03 UTC
Q&A  > regular expressions


I am trying to write a regular expression to aid in the parsing of a configuration file and I want to allow the users of the configuration file to specify any character in their directive including the special characters for the file format (comment (#), equivalance (=), etc.) and I have been trying to write an appropriate regex with no success. I am new at this and I have tried:
which represents a # not followed by an odd number of \'s (since \\# is the \ character metaquoted followed by a comment) but that didn't work becasue ^ only represents single characters and not sets of characters. I then tried the perl 5.005 negative lookbehind (?<!) but it only allows fixed width lookbehinds and I want to allow any number of \'s. Currently I am doing:
split /\Q#\E/; $_ = $_[0]; if(/\A\s*\Z/) { next; } $string = $_; for($i = 1; $i <= $#_; $i++) { $_ = $_[$i - 1]; m/(.)((\\){2})*\Z/; if("$1" eq "\\") { $string .= "\#" . $_[$i]; } else { last; } }
Can anyone suggest a regex to do all that work? I remember seeing one to correctly parse a C string somewhere which would deal with these same issues, but hard as I look I cannot find it.


Answer: How do I write a regex which allows meta-quoting?
contributed by WHolcomb

Quite nearly there. All that is left is that things in brackets like array subscripts are made into links to other nodes. That ought to be fixable by replacing them with the html codes, which I don't know off the top of my head. Ahh, they are &#91; -> [ and &#93; -> ]

To the monks who maintain this monestary I might suggest that they have the node linking ignore []'s inside <pre>'s.



$c = "\#";
$m = "\\";

while(<IN>) {
  split /\Q$c\E/;
  $_ = $_[0];
  next if(/\A\s*\Z/);
  $string = $_;
  for($i = 1; $i <= $#_; $i++) {
   $_ = $_[$i - 1];
   if("$1" eq "$m") {
     $string .= "$c" . $_[$i];
   } else {

Please (register and) log in if you wish to add an answer

  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?

    What's my password?
    Create A New User
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others making s'mores by the fire in the courtyard of the Monastery: (2)
    As of 2018-08-19 15:23 GMT
    Find Nodes?
      Voting Booth?
      Asked to put a square peg in a round hole, I would:

      Results (186 votes). Check out past polls.