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perl : question about defined()

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# 1  
Old 06-09-2010
perl : question about defined()
Hi there

rather than doing this
Code:
if (defined($new)) {
    unless (defined($hostname)) {
        print "ERROR: If using --new, you must define a hostname\n";
        exit 1;
    }
}


is there some way of doing a "notdefined" (i appreciate there is no such thing Smilie)


Code:
 if (defined($new) && notdefined($hostname)) {
        print "ERROR: If using --new, you must define a hostname\n"; 
        exit 1;
 }


any advise would be great
# 2  
Old 06-09-2010
Hi,

Code:
If ( ! defined $var)  { print "test" ; }

# 3  
Old 06-09-2010
Thanks pravin27, this works fine

Code:
        if (defined($new) && ( ! defined $hostname)) {
                        print "ERROR: If using --new, you must define a hostname\n";
                        exit 1;
        }




Actually, just playing around ...this seems to work


Code:
        if (defined($new) && (defined($hostname) eq "")) {
                        print "ERROR: If using --new, you must define a hostname\n";
                        exit 1;
        }

# 4  
Old 06-09-2010
Hi,

You missed one closing bracket of IF .

Code:
 if (defined($new) && ( ! defined $hostname) ) {
                        print "ERROR: If using --new, you must define a hostname\n";
                        exit 1;
        }

Last edited by Franklin52; 06-09-2010 at 10:44 AM.. Reason: adding code tags
# 5  
Old 06-09-2010
Quote:
Originally Posted by hcclnoodles
...
is there some way of doing a "notdefined" (i appreciate there is no such thing Smilie)

Code:
 if (defined($new) && notdefined($hostname)) {
        print "ERROR: If using --new, you must define a hostname\n"; 
        exit 1;
 }

...
While there is no such operator as notdefined, the Logical Not - not defined would work for your case. That's because not unary operator is the equivalent of the ! operator(except for the precedence).

Code:
$
$ perl -le '$new="x"; if(defined($new) && ! defined($hostname)){print "ERROR: If using --new, you must define a hostname"}'
ERROR: If using --new, you must define a hostname
$
$ perl -le '$new="x"; if(defined($new) && not defined($hostname)){print "ERROR: If using --new, you must define a hostname"}'
ERROR: If using --new, you must define a hostname
$

tyler_durden
# 6  
Old 06-09-2010
thanks pravi27 (you were very quick, i realised i missed a bracket and edited the post pretty quickly) Smilie


Tyler , thanks for the explanation, it is clear now Smilie
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