Testing for filled-in box with CGI::param() ?

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

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Re: Lexical variables question by davorg (Chancellor) on Aug 12, 2003 at 14:13 UTC
No. If it's possible for `param` to return "undef" then `defined $var` can be false. -- <http://www.dave.org.uk> "The first rule of Perl club is you do not talk about Perl club." -- Chip Salzenberg	[reply]
Re: Re: Lexical variables question by sweetblood (Prior) on Aug 12, 2003 at 14:18 UTC
But only a return of "undef" will cause defined to be false, anything else and $var is still defined, even a blank.	[reply]
Re: Lexical variables question by Abigail-II (Bishop) on Aug 12, 2003 at 14:14 UTC
No. `$var` has the value of whatever `param('search_string')` returns. If that function returns an undefined value, the condition in the if statement will be false. This has nothing at all to do whether `$var` is a lexical variable or not. Abigail	[reply]
Re: Lexical variables question by edan (Curate) on Aug 12, 2003 at 15:00 UTC
perldoc CGI states: If a value is not given in the query string, as in the queries "name1=&name2=" or "name1&name2", it will be returned as an empty string. This feature is new in 2.63. So, assuming you're using version 2.63 or later, and assuming that the parameter is being passed in the query string, only with no value (as in 'search_string=&blah_blah_blah=bar'), you'll want this instead of what you're using: `if ($var ne '')` [download] On a side note, as I was testing the above statement of CGI.pm, I found that if the parameter is the only thing in the query string, and has no value, then `param()` returns `undef` instead of the expected `''` empty string. Anyone know of a reason for this? Is it a bug, or is it expected behavior? I tested with CGI 2.752 `echo "foo" \| perl -MCGI=param,-debug -le'defined param("foo") and prin +t "defined!"' # doesn't print defined! ?? echo "foo=" \| perl -MCGI=param,-debug -le'defined param("foo") and pri +nt "defined!"' echo "foo&" \| perl -MCGI=param,-debug -le'defined param("foo") and pri +nt "defined!"' echo "&foo" \| perl -MCGI=param,-debug -le'defined param("foo") and pri +nt "defined!"' # these all print defined!` [download] HTH -- 3dan	[reply] [d/l] [select]
Re^2: Lexical variables question by Aristotle (Chancellor) on Aug 13, 2003 at 00:24 UTC
`if ($var ne '')` [download] That will emit a warning. You need to test definedness first. Makeshifts last the longest.	[reply] [d/l]
Re: Lexical variables question by dragonchild (Archbishop) on Aug 12, 2003 at 14:19 UTC
`$var` will be defined, but false. Try `if ($var)` instead. ------ We are the carpenters and bricklayers of the Information Age. The idea is a little like C++ templates, except not quite so brain-meltingly complicated. -- TheDamian, Exegesis 6 Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.	[reply] [d/l] [select]
Re: Re: Lexical variables question by edan (Curate) on Aug 12, 2003 at 15:24 UTC
In addition to davorg's valid criticism, your `if ($var)` test is less-than-optimal if zero is a valid value for the param, which it probably is... -- 3dan	[reply]
Re: Re: Lexical variables question by davorg (Chancellor) on Aug 12, 2003 at 14:34 UTC
`$var` will be defined, but false. Try `if ($var)` instead. Why do you think that `$var` can't be "undef"? If `param` returns "undef" then `$var` will be undefined. -- <http://www.dave.org.uk> "The first rule of Perl club is you do not talk about Perl club." -- Chip Salzenberg	[reply]
Re3: Lexical variables question by dragonchild (Archbishop) on Aug 12, 2003 at 15:25 UTC
Because it won't be undef from a checkbox. That was the real question from the OP. It will be undef if the name is wrong. It will be defined if the name is there and is a checkbox. It will be ''. ------ We are the carpenters and bricklayers of the Information Age. The idea is a little like C++ templates, except not quite so brain-meltingly complicated. -- TheDamian, Exegesis 6 Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.	[reply]
Re: Re3: Lexical variables question by davorg (Chancellor) on Aug 12, 2003 at 15:35 UTC
Re5: Lexical variables question by dragonchild (Archbishop) on Aug 12, 2003 at 16:35 UTC