in reply to extracting a substring from a string - multiple variables

Nobody answered after 16 min? Oh, graff did (and was faster than me) ;-)

 ...
 my ($fiop, $length, $data)
    = $string =~ m{<file                 # tag anchor
                   \s+ fiop="([^"]+)"    # (foo)
                   \s+ length="([^"]+)"  # (bar)
                   />                    # end: start file tag
                   \s* (.*?)             # (baz) - note the "nongreedy
+ness" .*?
                   </file>               # end: file tag
                  }x;

 print "$fiop, $length, $data\n";
 ...

[download]

Addendum: forgot the tag-cleaning part:

 
  ...
 (my $notags = $string) =~ s{<file.+?</file>}{};
  print "$notags\n";
  ...

[download]

Your mistake was basically to take the "greedy modifier" (.*), which matches until the end of the string - and backtracks then - and matches from the rear ...

Regards

mwa

Replies are listed 'Best First'.
Re^2: extracting a substring from a string - multiple variables
by walinsky (Scribe) on Oct 27, 2007 at 23:23 UTC
    I'm not sure if I should rephrase...
    The data I get is from a POST request; it's almost XML except for the <file/> part that I need take out, as parser.pm barfs on it..
    in "<file fiop="foo" length="bar"/>baz</file>", baz is raw binary;
    that's why (I think) the preg matching (m^) doesn't work.
    FYI baz looks like: µÜ¡3õ§©AEurope/Amsterdam$...
[reply]
      Ohh, *if* there is some binary within the tag and *if* the "length" field says sth. about its *length* you could easily construct a regex that extracts binary data of that length: 
       my $binary = pack 'F*', (3.141592) x 10;  # make binary vector of len
+gth 80 bytes
 my $string = '...blah...<file fiop="foo" length="' . length($binary) 
+.'"/>' . $binary . '</file>...blah...';

 my ($fiop, $length, $data)
    = $string =~ m{<file                   # tag anchor
                   \s+ fiop="([^"]+)"      # (fiop)
                   \s+ length="([^"]+)"    # (length)
                   />                      # end: start file tag
                   ((??{ "\\C{$2}" }))     # self modifying regex for 
+binary stuff
                   </file>                 # end: file tag
                  }sx;

 print "$fiop, $length (data comes below)\n";
 print join ',', unpack("F*", $data);      # extract binary data again
 
 (my $notags = $string) =~ s{<file.+</file>}{};
 print "\n$notags\n";

      [download]

      In the above I pack a binary sequence of 10 Pi-Numbers (double, 10 x 8 bytes) into the tag, match a binary sequence of its length ($2) and unpack it afterwards.

      Regards

      mwa

[reply]
[d/l]
        seems like graff was faster again ;)
        I did like your approach though!
        I'm not quite sure if (in your solution) $binary is known - in my case I'm handling POSTed data, where $length is declared in the data, and $binary just sits between the <file/> tags.
        Still; if $length and $binary could be extracted, unpack sounds more logical to me.
[reply]
        Seems like we're getting somewhere now; the code throws an error though, when applying the regex:
        Quantifier in {,} bigger than 32766 in regex; marked by <-- HERE in m/\\C{ <-- HERE 304507}/

        any idea ?
[reply]

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