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Allow empty form fields regex

by Hissingsid (Sexton)
on Mar 18, 2004 at 15:36 UTC ( #337704=perlquestion: print w/replies, xml ) Need Help??
Hissingsid has asked for the wisdom of the Perl Monks concerning the following question:

Hi,
I'm using a regex to allow input of some HTML markup into a form field but the field is still acceptable if it is empty. Here is what I'm using which seems to be validating in the way I want it to except if the field is empty then I get a false.

if ($contents != /^[\w \.\,\=\" \/<>]+$/ ){ $contentserror = "Error - message.";++$error; }

My question is: Can you please give me an example of how I can allow the field to be empty but only validate against the regex above if it has any characters in it.

I guess I could hack it by saying this first

if ($contents = ""){ $contents = "\s"; }

and then put it through the regex but that is a real mess.

Any ideas, I've done a few searches but can't find anything to help me out there.

Many thanks
Sid

20040318 Edit by Corion: Added code tags

Replies are listed 'Best First'.
Re: Allow empty form fields regex
by matija (Priest) on Mar 18, 2004 at 16:12 UTC
    Well, at first I wanted to say you only need to add a |(^$) to your regexp, but some experimentation has showed me that doesn't work.

    Then I took a good look at you regexp. You are accepting any of a class of characters, one or more times. To accept an empty field as well, simply change the + to *:

    if ($contents != /^[\w \.\,\=\" \/<>]*$/ ){ $contentserror = "Error - message.";++$error; }
    It's not a general answer, but in your particular case, it should work.
      Hi,

      Thanks for the excellent input.

      I played around a bit and this is what I have got working perfectly.

      if (($contents ne "") && (!($contents =~ /^[\w \.\,\=\" \/<>]+$/))){ $contentserror = "Error - message.";++$error; }
      For some reason this != was not helping the situation.

      Anyway Paladin, a big thanks I had been fiddleing for hours and now have a good solution thanks to your suggestion.

      Best wishes

      Sid

      Edit by castaway, added code tags

        Apologies guys I missed the bit about !=/!~

        !~ does indeed work removing the need for some of the ()s.

        Many thanks Sid
Re: Allow empty form fields regex
by Paladin (Priest) on Mar 18, 2004 at 16:08 UTC

    First, the operator to bind a regex match to a variable is =~ and to negate that, it's !~

    Second, the operator to compare strings is eq. = is the assignment operator.

    Now that that's out of the way, you could do something like:

    if ( ($contents ne "") && ($contents !~ /^[\w \.\,\=\" \/<>]+$/) ){ $contentserror = "Error - message.";++$error; }
    This will first check if $contents is not empty, and if it's not, then check it against the regex, and if the regex doesn't match, then execute the body of the if statement.
Re: Allow empty form fields regex
by tcf22 (Priest) on Mar 18, 2004 at 16:07 UTC
    How about this
    if ((length($contents) > 0) && ($contents !~ /^[\w \.\,\=\" \/<>]+$/)) +{ $contentserror = "Error - message.";++$error; }
    Also != should probably be !~.

    - Tom

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[jdporter]: one prog I have has a UI which allows to input a bit mask
[jdporter]: currently it expects the bitmask to be in the form of a hex number, e.g. 0x0101
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[jdporter]: let me google that for me ;-)
[jdporter]: hex points explicitly to oct, which does the job. :-D
[jdporter]: omg, I f love Perl!

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