On Mon, 4 Jun 2001, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote,
> if ( $formdata{view_name} ne "" ) {
> $view = $formdata{view_name};
> $viewtag = "1";
> }
>
> is there a special method for testing against a null string for a form
> field's value? i am using the above data, but it seems to always return
> with a value of "1" making me think that something is incorrect in my if
> test. the form itself does not have anything default value specified for
> view_name.
Take a look at these one-liner examples. The string "(nothing)" indicates
that no output is printed.
1% perl -le '$x; print 1 if $x ne ""'
(nothing)
2% perl -le '$x = undef; print 1 if $x ne ""'
(nothing)
3% perl -wle '$x = undef; print 1 if $x ne ""'
Use of uninitialized value at -e line 1.
4% perl -wle '$x = "i am here"; print 1 if $x ne ""'
1
5% perl -we '$x = undef; print "($x)\n";
Use of uninitialized value at -e line 1.
()
6% perl -we '$x = ""; print "($x)\n";
()
Number 2 is basically same with number 1 in that $x is undefined,
except that $x variable in the number 2 is explicitly assigned.
(Number 1 will also give you extra warning if you use -w).
The line under number 3 is not an output of the code, it's a
warning that will guide you what's wrong with the code.
Undefined value is not the same as empty string (""), but both are
evaluated to false. If you use undefined variable anyway, it will be
evaluated to empty (see no.5 and 6). Empty field is sent as undefined
value and when you test it against "" with 'ne' operator, it evaluates to
true because they're not equal.
You need the defined() function to test whether the variable contains
some defined value, and it will cover both "" and 0 if the test returns
true.
if (defined $var) {
....
}
If you need the value of the variable and you don't want "" then you
need to test that too,
if (defined $var and $var ne "") {
....
}
or
if (defined $var and length $var) {
....
}
But if you rather want to test $var against true value, you can simply
use,
if ($var) {
....
}
Btw, did you use -w switch and use strict in your script?
You really should. All those example codes above will bail out when
you use strict.
hth
s.a.n
--
Hasanuddin Tamir: [EMAIL PROTECTED] - Trabas: www.trabas.com
