RE: help with defined and !not defined
> -Original Message-
> From: lorid
> Im want to set the $photo_year and $photo_month to another
> value if it
> is not already set.
>
> my $ARGV[0] will sometimes be passed a string like
> this:nvIGRA with no
> date at end and sometimes with date nvIGRA200511
> if it does not have date I need to set it another way but cant get
> syntax of !defined
>
this will work:
my $filename = $ARGV[0];
if ( $filename =~ /nvIGRA(\d{4})(\d{2})/ ) {
my $photo_year=$1;
my $photo_month=$2;
}
$photo_year=2005 unless defined $photo_year;
$photo_month=7 unless defined $photo_month;
if ($photo_month<10) {
$photo_month="0".$photo_month;
}
note: if you can have other strings other than "nvIGRA" change that
part into a regular expression.
>
>
> my $filename = $ARGV[0];
> my $photo_year;
> $photo_year= substr($filename,6,4);
> my $photo_month ;
> $photo_month= substr($filename,10,2);
> #This just blows my web page
> if(!defined $photo_year){
> $photo_year ="2005";
> }
>
>
> #I have also tried
> if(defined $qphoto_year){
>#test
>$test1 ="Im defined";
> }
> else{
> $test2 ="Im Not defined";
> print "$test2";
>}
>
> How come It always returns Im defined ,even when no date is
> passed should I do some kind of checking on my $ARGV[0]
> before doing the
> asignment $photo_year= substr($filename,6,4);
>
>
> help appreciated
>
> thanks
> lori
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Re: help with defined and !not defined
On Fri, 22 Jul 2005 12:05:16 -0700, you wrote: >You want to check if it's null, not if it's defined. Defined means that the >variable exists. Almost. Defined means the variable exists AND its value is not undef, as this snippet demonstrates: my $foo; print !defined $foo; As for the OP's question, substr() does indeed return undef if the offset and length specification refers to something completely outside the string argument. I suspect that the elements of @ARGV have newlines or other whitespace at the end that are causing a problem. -- Eric Amick Columbia, MD ___ Perl-Win32-Users mailing list Perl-Win32-Users@listserv.ActiveState.com To unsubscribe: http://listserv.ActiveState.com/mailman/mysubs
Re: help with defined and !not defined
I see, that's a really bad example and I can see why it would confuse.
Variables in perl don't have a true "undefined state" like say C might.
Because of autovivification, *all* variables are in a state of potential
existence. Once u reference a variable, it comes into existence with the
undefined value. defined() see's if a variable has the undef value or
something else, including null. So in ur example below it should be "a's
value is not undef" not "a has a value". In perl "defined" means "has
anything every been assigned to x".
At 07:27 AM 7/22/05 -0700, lorid wrote:
>you are right about I should test for null or length of value instead but
>I found the place where I got information that says that to be defined a
>var must have a value:
>Beginnng Perl by Simon Cozens pg 123:
>
>"We can test if a variable is defined by...
>my $a;
>my $b;
>$b = 10;
>if (defined $a){
> print "a has a value.\n";
>}
>if (defined $b){
> print "b has a value.\n";
>}
>#only prints b has a value
--
REMEMBER THE WORLD TRADE CENTER ---=< WTC 911 >=--
"...ne cede males"
0100
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RE: help with defined and !not defined
Title: Re: help with defined and !not defined
lorid wrote, on Fri 7/22/2005 10:27: my $a;: my $b;:: $b = 10;:: if
(defined $a){
All well and good; but in your
original post (which I no longer have available to quote, but I believe I recall
correctly), your $a (or equivalent) was the result of a substr operation. So it
has, in fact, been assigned a value (the desired portion of the string). What
you *want* to test is if that portion is the zero-length string, hence the
length() function is what you need in this case.
Defined is for cases where
nothing has actually been assigned, such as when a regex fails (or doesn't have
enough matches to fill all the variables, or one alternation is chosen over
another):
/("[^"]*")|(.*)/;
if (defined($1)) { #strip the
quotes
See?
Good luck,
Joe
==
Joseph P. Discenza, Sr.
Programmer/Analyst
mailto:[EMAIL PROTECTED]
Carleton Inc. http://www.carletoninc.com
574.243.6040 ext. 300 fax: 574.243.6060 Providing
Financial Solutions and Compliance for over 30 Years
From:
[EMAIL PROTECTED] on behalf of
loridSent: Fri 7/22/2005 10:27To: Chris
WagnerCc: perl-win32-usersSubject: Re: help with defined
and !not defined
Chris Wagner wrote:>You want to check if it's null,
not if it's defined. Defined means that the>variable exists.
You want something like if ($photo_year) {...}.>>At 01:48 PM
7/21/05 -0700, lorid wrote:> >>>my $ARGV[0]
will sometimes be passed a string like this:nvIGRA with no>>date at
end and sometimes with date nvIGRA200511>>if it does not have date I
need to set it another way but cant get>>syntax of
!defined>> >>>> >you
are right about I should test for null or length of value instead butI found
the place where I got information that says that to be defined avar must
have a value:Beginnng Perl by Simon Cozens pg 123:"We can test if a
variable is defined by...#!/usr/bin/perluse strict;#use
warnings;my $a;my $b;$b = 10;if (defined
$a){ print "a has a value.\n";}if (defined $b){
print "b has a value.\n";}#only prints b has a
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Re: help with defined and !not defined
Chris Wagner wrote:
You want to check if it's null, not if it's defined. Defined means that the
variable exists. You want something like if ($photo_year) {...}.
At 01:48 PM 7/21/05 -0700, lorid wrote:
my $ARGV[0] will sometimes be passed a string like this:nvIGRA with no
date at end and sometimes with date nvIGRA200511
if it does not have date I need to set it another way but cant get
syntax of !defined
you are right about I should test for null or length of value instead but
I found the place where I got information that says that to be defined a
var must have a value:
Beginnng Perl by Simon Cozens pg 123:
"We can test if a variable is defined by...
#!/usr/bin/perl
use strict;
#use warnings;
my $a;
my $b;
$b = 10;
if (defined $a){
print "a has a value.\n";
}
if (defined $b){
print "b has a value.\n";
}
#only prints b has a value
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RE: help with defined and !not defined
"if ($photo_year)" simply tests for a true value and will behave incorrectly if
$photo_year is "0". What you really mean is "if (!length $photo_year)".
-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] Behalf Of
Chris Wagner
Sent: Thursday, July 21, 2005 3:03 PM
To: perl-win32-users
Subject: Re: help with defined and !not defined
You want to check if it's null, not if it's defined. Defined means that the
variable exists. You want something like if ($photo_year) {...}.
At 01:48 PM 7/21/05 -0700, lorid wrote:
>my $ARGV[0] will sometimes be passed a string like this:nvIGRA with no
>date at end and sometimes with date nvIGRA200511
>if it does not have date I need to set it another way but cant get
>syntax of !defined
--
REMEMBER THE WORLD TRADE CENTER ---=< WTC 911 >=--
"...ne cede males"
0100
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Re: help with defined and !not defined
You want to check if it's null, not if it's defined. Defined means that the
variable exists. You want something like if ($photo_year) {...}.
At 01:48 PM 7/21/05 -0700, lorid wrote:
>my $ARGV[0] will sometimes be passed a string like this:nvIGRA with no
>date at end and sometimes with date nvIGRA200511
>if it does not have date I need to set it another way but cant get
>syntax of !defined
--
REMEMBER THE WORLD TRADE CENTER ---=< WTC 911 >=--
"...ne cede males"
0100
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help with defined and !not defined
Im want to set the $photo_year and $photo_month to another value if it
is not already set.
my $ARGV[0] will sometimes be passed a string like this:nvIGRA with no
date at end and sometimes with date nvIGRA200511
if it does not have date I need to set it another way but cant get
syntax of !defined
my $filename = $ARGV[0];
my $photo_year;
$photo_year= substr($filename,6,4);
my $photo_month ;
$photo_month= substr($filename,10,2);
#This just blows my web page
if(!defined $photo_year){
$photo_year ="2005";
}
#I have also tried
if(defined $qphoto_year){
#test
$test1 ="Im defined";
}
else{
$test2 ="Im Not defined";
print "$test2";
}
How come It always returns Im defined ,even when no date is passed
should I do some kind of checking on my $ARGV[0] before doing the
asignment $photo_year= substr($filename,6,4);
help appreciated
thanks
lori
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