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Hi

How do I pass a hash to another script via the command line?

That is, if I do this

use strict;
my %data = (
field1 => 'f1val',
field2 => 'f2val'
);
my $result = `perl z:/interface.pl \%data`;

and in interface.pl I have the lines:

use strict;
my($dataref) = $ARGV[0];
print $dataref->{'field1'};

I get the error:

Can't use string ("%data") as a HASH ref while "strict refs" in use at
z:/interface.pl line ..

and if I comment out "use strict" then I get nothing.

What am I doing wrong?

Thanks
Ian

IanW wrote:
> How do I pass a hash to another script via the command line?
[sample script snipped, thank you for providing it]
> What am I doing wrong?

The shell command line argument interface does not provide any means to pass
complex data structures like hashes or references. It can deal with simple
strings only. This is not a limitation of Perl but of the command shell.

In other words: you need to pass the actual keys and values of your hash (as
strings!) and then recompose them into a hash in the called program.

It might be easier to use Data:umper to convert the hash into a textual
representation that can readily loaded into perl again or to use some other
form of interprocess communication.

jue

"IanW" <> wrote in message
news:f58nbp$muc$1$...

>
> and if I comment out "use strict" then I get nothing.
>
> What am I doing wrong?

I should say I am doing a "print $result;" in the calling script!

IanW ha scritto:

> Hi
>
> How do I pass a hash to another script via the command line?
>

You can't.

> What am I doing wrong?
>
> Thanks
> Ian

Possible workaround: you can try to tie-untie your hash to a file so
you can pass the filename to the second script which can tie-untie the
same hash, then.

"Jürgen Exner" <> wrote in message
news:XoRdi.7443$u65.1117@trndny07...

> It might be easier to use Data:umper to convert the hash into a textual
> representation that can readily loaded into perl again

Hi Jue

Thanks for the reply.

If I understand it correctly, doesn't Data:umper just convert the hash
into a string representing the hashes structure? In which case, if I tried
to pass that via the command line, the spaces (amongst some other characters
like double quotes) would cause probs when the string is pulled into @ARGV
at the receiving script?

Eg:

use Data:umper;
my $d = Dumper(\%data);
my $result = `perl z:/interface.pl $d`;

That would result in only $ARGV[0] only containing "$VAR1". One could put $d
in double quotes, but if there were double quotes in one of the hash values
then it would presumably mess things up again.

Regards
Ian

"mattsteel" <> wrote in message
news: oups.com...

> Possible workaround: you can try to tie-untie your hash to a file so
> you can pass the filename to the second script which can tie-untie the
> same hash, then.

I was rather hoping avoiding passing data via a file but thanks anyway.

Regards
Ian

IanW wrote:
> How do I pass a hash to another script via the command line?

As others have told you, you can't.

However, nothing prevents you from assigning a hashref to @ARGV
directly, i.e. instead of

> my $result = `perl z:/interface.pl \%data`;

you may want to try:

$ARGV[0] = \%data;
do 'z:/interface.pl';

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

IanW wrote:

>
> "Jürgen Exner" <> wrote in message
> news:XoRdi.7443$u65.1117@trndny07...
>
>> It might be easier to use Data:umper to convert the hash into a textual
>> representation that can readily loaded into perl again
>
> Hi Jue
>
> Thanks for the reply.
>
> If I understand it correctly, doesn't Data:umper just convert the hash
> into a string representing the hashes structure? In which case, if I tried
> to pass that via the command line, the spaces (amongst some other
> characters like double quotes) would cause probs when the string is pulled
> into @ARGV at the receiving script?
>
> Eg:
>
> use Data:umper;
> my $d = Dumper(\%data);
> my $result = `perl z:/interface.pl $d`;
>
> That would result in only $ARGV[0] only containing "$VAR1". One could put
> $d in double quotes, but if there were double quotes in one of the hash
> values then it would presumably mess things up again.
>
> Regards
> Ian

I think there is a simple point being missed here.

Why not use Data:umper to serialise the data (because that's what it
does), print the result to STDOUT, have the called program read it in from
STDIN to a scalar, then eval the scalar.

In other words, pipe the serialised version of the hash between the two
programs. Very much the "unix way" (TM).

Another way to do it would be to use IPC::Shareable and tie the hash to a
blob of shared memory. All that the callee program needs to know is the
shared memory key id which is trivially passed as an argument.

Probably not a lot efficiency wise as the latter method has to serialise the
data anyway, but it's neat, and potentially bi-directional - ie the callee
can modify the data and have the caller see it.

Cheers

Tim

Purl Gurl <> wrote:
> IanW wrote:
>
>> How do I pass a hash to another script via the command line?

> Others have explained why you cannot do this.

> I would simply
> create an array, pass the array, then work with array @ARGV
> in my secondary script, without creating a new hash.
>
> PRIMARY:
>
> #!perl
>
> %Data = (field1 => 'f1val', field2 => 'f2val', field3 => 'f3val');


Try it with these values:

%Data = (field1 => 'f1 val', field2 => 'f2val', field3 => 'f3val');

then rethink your "solution".


> system ("perl test2.pl @{[%Data]}");


--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.noitatibaher\100cmdat/"

"Gunnar Hjalmarsson" <> wrote in message
news:...
> IanW wrote:
>> How do I pass a hash to another script via the command line?
>
> As others have told you, you can't.
>
> However, nothing prevents you from assigning a hashref to @ARGV directly,
> i.e. instead of
>
>> my $result = `perl z:/interface.pl \%data`;
>
> you may want to try:
>
> $ARGV[0] = \%data;
> do 'z:/interface.pl';

I did want, I did try and it did work

I had actually found another way that seemed to work, just before I read
your post, and that was to use Data:umper to stringify the hash, then
MIME::Base64 to encode it, then remove the line breaks, and then pass the
resulting string via the command line to then decode it at the other end.

However your way it decidedly simpler thanks.

Thanks also for the other responses. One thing I noticed from the different
replies is that there seem to be 3 ways to call another Perl script - the
backticks that I used, 'system', and 'do' - are there any real differences
between them?

Ian