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empty variables - getting rid of "uninitialized value" warnings? Tomasz Chmielewski 03-28-2008
Posted by Tomasz Chmielewski on March 28, 2008, 5:34 am
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 I have perl code which should do some action only if:

- the variable does not begin with "#" (commented out),
- the variable is not empty



use strict;
use warnings;

my @array = ("# Comment", "/usr/bin/binary --test", "");

foreach my $var (@array) {

my @execargs = split(/#/, $var);

if ( $execargs[0] ne '' ) { print "$var 0: |$execargs[0]|\n" }

}


Unfortunately, it shows uninitialized value warnings for the empty
variable (""):

$ perl test.pl
/usr/bin/binary --test 0: |/usr/bin/binary --test|
Use of uninitialized value $execargs[0] in string ne at test.pl line 14.



Using:

if ( defined $execargs[0] ) { print "$var 0: |$execargs[0]|\n" }

is not a solution either, because $execargs[0] will be defined for a
case with "# Comment" and an undesired action will be made for this element:


$ perl test.pl
# Comment 0: ||
/usr/bin/binary --test 0: |/usr/bin/binary --test|



How can I get rid of warnings if I make tests with "if" and some
variables are empty?

Should I just ignore it? Or use "no warnings" just for that piece of
code throwing a warning?



--
Tomasz Chmielewski
http://wpkg.org

Posted by Gunnar Hjalmarsson on March 28, 2008, 6:16 am
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 Tomasz Chmielewski wrote:
> I have perl code which should do some action only if:
>
> - the variable does not begin with "#" (commented out),
> - the variable is not empty
>
> use strict;
> use warnings;
>
> my @array = ("# Comment", "/usr/bin/binary --test", "");
>
> foreach my $var (@array) {
>
> my @execargs = split(/#/, $var);
>
> if ( $execargs[0] ne '' ) { print "$var 0: |$execargs[0]|\n" }
>
> }
>
> Unfortunately, it shows uninitialized value warnings for the empty
> variable (""):
>
> $ perl test.pl
> /usr/bin/binary --test 0: |/usr/bin/binary --test|
> Use of uninitialized value $execargs[0] in string ne at test.pl line 14.
>
> Using:
>
> if ( defined $execargs[0] ) { print "$var 0: |$execargs[0]|\n" }
>
> is not a solution either, because $execargs[0] will be defined for a
> case with "# Comment" and an undesired action will be made for this
> element:
>
> $ perl test.pl
> # Comment 0: ||
> /usr/bin/binary --test 0: |/usr/bin/binary --test|
>
> How can I get rid of warnings if I make tests with "if" and some
> variables are empty?
>
> Should I just ignore it? Or use "no warnings" just for that piece of
> code throwing a warning?

foreach my $var (@array) {
next unless defined $var and length $var;
next if substr($var, 0, 1) eq '#';
print "$var\n";
}

--
Gunnar Hjalmarsson
Email: http://www.gunnar.cc/cgi-bin/contact.pl

Posted by John W. Krahn on March 28, 2008, 8:04 am
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Tomasz Chmielewski wrote:
> I have perl code which should do some action only if:
>
> - the variable does not begin with "#" (commented out),
> - the variable is not empty
>
>
> use strict;
> use warnings;
>
> my @array = ("# Comment", "/usr/bin/binary --test", "");
>
> foreach my $var (@array) {
>
> my @execargs = split(/#/, $var);
>
> if ( $execargs[0] ne '' ) { print "$var 0: |$execargs[0]|\n" }
>
> }
>
>
> Unfortunately, it shows uninitialized value warnings for the empty
> variable (""):
>
> $ perl test.pl
> /usr/bin/binary --test 0: |/usr/bin/binary --test|
> Use of uninitialized value $execargs[0] in string ne at test.pl line 14.

$ perl -le'
use strict;
use warnings;
my @array = ( "# Comment", "/usr/bin/binary --test", "" );
foreach my $var ( @array ) {
next if $var =~ /^(?:#|$)/;
print $var;
}
'
/usr/bin/binary --test




John
--
Perl isn't a toolbox, but a small machine shop where you
can special-order certain sorts of tools at low cost and
in short order. -- Larry Wall

Posted by Jim Cochrane on March 28, 2008, 2:57 pm
Please log in for more thread options
> I have perl code which should do some action only if:
>
> - the variable does not begin with "#" (commented out),
> - the variable is not empty
>
>
>
> use strict;
> use warnings;
>
> my @array = ("# Comment", "/usr/bin/binary --test", "");
>
> foreach my $var (@array) {
>
> my @execargs = split(/#/, $var);
>
> if ( $execargs[0] ne '' ) { print "$var 0: |$execargs[0]|\n" }
>
> }

If I understand what you're trying to do (and perhaps I don't), you want
something like this:

#!/usr/bin/perl

use strict;
use warnings;

my @array = ("# Comment",
        "/usr/bin/binary --test1",
        "/usr/bin/binary --test2",
        "/usr/bin/binary\t--test3",
        " /usr/bin/binary --test4",
        "");

for my $var (@array) {
        if (not $var or $var =~ /^#/) {
                next;
        }
        my @execargs = split(' ', $var);
        print 'arg array: ' . join(', ', @execargs) . "\n";
}


>
>
> Unfortunately, it shows uninitialized value warnings for the empty
> variable (""):
>
> $ perl test.pl
> /usr/bin/binary --test 0: |/usr/bin/binary --test|
> Use of uninitialized value $execargs[0] in string ne at test.pl line 14.
>
>
>
> Using:
>
> if ( defined $execargs[0] ) { print "$var 0: |$execargs[0]|\n" }
>
> is not a solution either, because $execargs[0] will be defined for a
> case with "# Comment" and an undesired action will be made for this element:
>
>
> $ perl test.pl
> # Comment 0: ||
> /usr/bin/binary --test 0: |/usr/bin/binary --test|
>
>
>
> How can I get rid of warnings if I make tests with "if" and some
> variables are empty?
>
> Should I just ignore it? Or use "no warnings" just for that piece of
> code throwing a warning?
>
>
>


--


Posted by Willem on March 28, 2008, 3:18 pm
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Tomasz wrote:
) I have perl code which should do some action only if:
)
) - the variable does not begin with "#" (commented out),
) - the variable is not empty

That's not quite what your code indicates is your intention.

It looks more like:
- Print only the part of a line before the '#'
- Don't print of the above is empty.


) my @array = ("# Comment", "/usr/bin/binary --test", "");
)
) foreach my $var (@array) {
)
) my @execargs = split(/#/, $var);
)
) if ( $execargs[0] ne '' ) { print "$var 0: |$execargs[0]|\n" }
)
) }
)
)
) Unfortunately, it shows uninitialized value warnings for the empty
) variable (""):
)
) $ perl test.pl
) /usr/bin/binary --test 0: |/usr/bin/binary --test|
) Use of uninitialized value $execargs[0] in string ne at test.pl line 14.
)
)
)
) Using:
)
) if ( defined $execargs[0] ) { print "$var 0: |$execargs[0]|\n" }
)
) is not a solution either, because $execargs[0] will be defined for a
) case with "# Comment" and an undesired action will be made for this element:

How about just:

if ($execargs[0]) ?

And how about:
my ($execarg) = split(/#/, $var);
and then:
if ($execarg) { ... }


SaSW, Willem
--
Disclaimer: I am in no way responsible for any of the statements
made in the above text. For all I know I might be
drugged or something..
No I'm not paranoid. You all think I'm paranoid, don't you !
#EOT

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