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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;
}

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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";
}

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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;
}

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    It's not a general answer, but in your particular case, it should work.
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      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;
}

      [download]
      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

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

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

        Many thanks Sid
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Re: Allow empty form fields regex
by Paladin (Vicar) 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;
}

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

    [download]
    Also != should probably be !~.

    - Tom

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