testing for the zero length string (blank value) in cgi fields

scratch has asked for the wisdom of the Perl Monks concerning the following question:

Hello all,

I'm using CGI.pm to collect some user info through a series of web pages. I've been just writing the captured data out to a file, but now I'm trying to write to a database. For the most part this is working well, but for a few fields I'm trying to test for a value of 'blank' or 'no data' (this would be for fields left unanswered). By default perl seems to convert these to a value of 0, but I'd like to convert them to -1.

My problem is in testing for this blank value. I've tried lots of things, all of them more or less like this:

@negs = qw ( foo bar baz ); 
    foreach $neg (@negs) { 
      if (param('$neg') eq "") {    
         param(-name=>"$neg", -value=>-1)  ; 
      }
    }
[download]

This, however, replaces *all* values of foo, bar, and baz with -1, not just the blank values.

Is there a way I can test for the blank value? Is there a better way to achieve my goal of not allowing fields to be left blank by users, but recording a value of -1 in the database for these fields?

Thanks as always,

scratch

Comment on testing for the zero length string (blank value) in cgi fields Download Code

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Re: testing for the zero length string (blank value) in cgi fields by Masem (Monsignor) on Oct 24, 2001 at 17:49 UTC
This line: `if (param('$neg') eq "")` [download] is checking the param named "'$neg'"; that is, there is no expansion of the variable going on with single quotes, so you're not checking what you think you are checking. Ditch the quotes: `if (param($neg) eq "")` [download] and it should work. ----------------------------------------------------- Dr. Michael K. Neylon - mneylon-pm@masemware.com \|\| "You've left the lens cap of your mind on again, Pinky" - The Brain "I can see my house from here!" It's not what you know, but knowing how to find it if you don't know that's important	[reply] [d/l] [select]
Re: testing for the zero length string (blank value) in cgi fields by davorg (Chancellor) on Oct 24, 2001 at 18:35 UTC
A number of people have pointed out your problems with quotes, but no-one has yet simplified your test. If you change it to `if (param($neg)) {` [download] then you'll cover the case where the value isn't set, but also the case where the input doesn't exist. Update: blakem is absolutely right! -- <http://www.dave.org.uk> "The first rule of Perl club is you don't talk about Perl club."	[reply] [d/l]
Re: Re: testing for the zero length string (blank value) in cgi fields by blakem (Monsignor) on Oct 25, 2001 at 00:08 UTC
That's inverted... I think you mean: `unless (param($neg)) { # or if (!param($neg)) {` [download] -Blake	[reply] [d/l]
Re: testing for the zero length string (blank value) in cgi fields by jj808 (Hermit) on Oct 24, 2001 at 17:52 UTC
I think you may have a problem with your quotes. The line `if (param('$neg') eq "") {` [download] will not interpolate the value of $neg, so unless you have a parameter called '$neg' (with the dollar symbol) then this will always evaluate to true, hence trashing the values of your other parameters. Try it like this instead: `if (param($neg) eq "") {` [download] Cheers, JJ Update: Must learn to type as quickly as Masem :-)	[reply] [d/l] [select]
Re: testing for the zero length string (blank value) in cgi fields by tommyw (Hermit) on Oct 24, 2001 at 17:52 UTC
Ahem! You're testing param('$neg') (ie a parameter with the four character name $neg), but resetting the param(-name=>"$neg") (ie. one of foo, bar or baz). Change the quotes and the problem goes away.	[reply]