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

I think I may have hit on an undocumented CGI.pm feature, or at least one that I didn't know existed.

When a POST'd form is sent to a CGI.pm enabled script, apparently you can use the query_string() method to create a state-saving parameter list, suitable to be loaded into a new CGI.pm instance to restore the parameters at a later date.

My impression was that the query_string method returned the "unprocessed query string" (quoted from the docs), which led me to believe it returned $ENV{QUERY_STRING}.

Happily, this doesn't appear to be the case. Do other folks use/abuse this feature, and is it something I can rely upon?

-Any sufficiently advanced technology is
indistinguishable from doubletalk.

  • Comment on Interesting CGI.pm query_string behavior

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•Re: Interesting CGI.pm query_string behavior
by merlyn (Sage) on Aug 13, 2002 at 18:01 UTC
    I think your leap from "unprocessed query string" to $ENV{QUERY_STRING} is the mistake here. Since the model of CGI.pm is that it work nearly transparently for both GET and POST, I would never have imagined it to generate different results for query_string().

    So I presume, yes this is a feature, and yes, it's not going away soon.

    -- Randal L. Schwartz, Perl hacker

[reply]

      This behavior does seem consistent with how the rest of CGI.pm works.

      For some reason I had it in my head that methods like query_string() and script_name() were just convenience methods for getting %ENV values, but this isn't the case. Fine with me, because this is a very nice feature. . .The docs were just a bit confusing as to what was actually returned from query_string().

      Thanks.

      -Any sufficiently advanced technology is
      indistinguishable from doubletalk.

[reply]
        Indeed. It even becomes clearer when we look at the CGI.pm code. :) 

        #### Method: query_string
# Synthesize a query string from our current
# parameters
####
'query_string' => <<'END_OF_FUNC',
sub query_string {
    my($self) = self_or_default(@_);
    my($param,$value,@pairs);
    foreach $param ($self->param) {
        my($eparam) = escape($param);
        foreach $value ($self->param($param)) {
            $value = escape($value);
            push(@pairs,"$eparam=$value");
        }
    }
    return join($USE_PARAM_SEMICOLONS ? ';' : '&',@pairs);
}

        [download]

        - from CGI.pm

        So it simply constructs a query string from the given name/value pairs already in the CGI object. It'll even use that far-out semicolon format if you want it to. :)

[reply]
[d/l]

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