l i n u x - u s e r s - g r o u p - o f - d a v i s
Next Meeting:
July 7: Social gathering
Next Installfest:
Latest News:
Jun. 14: June LUGOD meeting cancelled
Page last updated:
2001 Dec 30 17:07

The following is an archive of a post made to our 'vox-tech mailing list' by one of its subscribers.

Report this post as spam:

(Enter your email address)
Re: [vox-tech] Perl: Checking if a hash exists and is true
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [vox-tech] Perl: Checking if a hash exists and is true

On Mon, Jul 09, 2001 at 02:39:15PM -0500, Jay Strauss wrote:
> I'm trying to check if a hash key exists and if the value is 1.  I'm passing
> the reference to the hash to a subroutine like:

> my $help = 1;
> my %hash = (help=>\$help);
> somefunc(\%hash);
> sub somefunc {
>     my ($refHash) = @_;
>     if ((defined $refHash->{help}&& ${$refHash->{help}}) {
>         # stuff
>     }
>     else {
>         # other stuff
>     }
> }

> This seems long an clumsy, I suspect there is a cleaner way to do it in perl
> but I don't know how.  I played around with "exists" but that just tells me
> that the value exists.  I need to do some processing if the value is "1" and
> other processing for "0";

my $help = 1;
my $hash = {help=>\$help};
#@@ change %hash to $hash, and (key=>val) to {key=>val}

sub somefunc {
    my ($refHash) = @_;
#@@ this is unchanged...

    if ((defined $refHash->{help}&& ${$refHash->{help}}) {
#@@ you might try the $$refHash->{help} syntax and see if that works for you.
#@@ (defined $refHash->{help}) will always be defined w/ the reference to
#@@ the variable regardless of $help's state, it's a pointless check.  
#@@ Add ${} or change to 'exists'... see below.
        # stuff
    else {
        # other stuff

any "bareword" inside a {} construct is treated as a hash key... not a
problem for 'use strict' at all.

also, make sure you look at "exists" as opposed to "defined"... exists
will tell you if a given key in a hash exists, while defined tells you if
a given variable has a "defined" value.  You can assign undef to a
variable, which would fail a defined check, but pass a exists check.
(looks like defined is correct for you, but you may need a ${} or $$
syntax to really check the variable and not the ref -- as the ref will
always be defined regardless of an undef state in the $help variable).

Ted Deppner

LUGOD Group on LinkedIn
Sign up for LUGOD event announcements
Your email address:
LUGOD Group on Facebook
'Like' LUGOD on Facebook:

Hosting provided by:
Sunset Systems
Sunset Systems offers preconfigured Linux systems, remote system administration and custom software development.

LUGOD: Linux Users' Group of Davis
PO Box 2082, Davis, CA 95617
Contact Us

LUGOD is a 501(c)7 non-profit organization
based in Davis, California
and serving the Sacramento area.
"Linux" is a trademark of Linus Torvalds.

Sponsored in part by:
O'Reilly and Associates
For numerous book donations.