Help with JSON Module

foggy3657 has asked for the wisdom of the Perl Monks concerning the following question:

Hi all, I am new to programming and Perl. I am using a an API to return JSON data/array/hash and from that I need to create a variable from part of the data in order to create my next URL. From a previous request for help I have been advised that I should use the JSON module. I have tried to follow an example taken from google, but clearly failing to grasp the program logic or syntax.

#!/usr/bin/perl
use warnings;
use strict;
use WebService::Tesco::API;
use JSON;

# My code to login removed


print "Scan Item....";
my $pn = <>;                                          #Scan Bar Code
chop ($pn);                                                          #
+remove %OA from end of scan code

my $code = $tesco->product_search({ searchtext => $pn, extendedinfo =>
+ 'N' });

my $json = JSON->new;
my $data = $json->decode($code);

my $pid = $data->{Products}[0]{ProductId},"\n";

print $pid,"\n";
[download]

Returned is:

Useless use of a constant (
) in void context at tesc_json1.pl line 22.
https://secure.techfortesco.com/groceryapi_b1/restservice.aspx?email=x
+xxxx%40yahoo.co.uk&password=xxxxx&developerkey=xxxxxx&applicationkey=
+xxxxx&command=LOGIN at /usr/local/share/perl/5.14.2/WebService/Tesco/
+API.pm line 59.
{
"StatusCode": 0,
"StatusInfo": "Command Processed OK",
"BranchNumber": "5528",
"CustomerId": "20846164",
"CustomerName": "Mr Stubbs",
"SessionKey": "5VApkMMTjO8LtFCy9VjcSrcZKxoewwHGj6XoUUGaH2fBWf73cU",
"InAmendOrderMode": "N",
"BasketID": "98911496",
"ChosenDeliverySlotInfo": "No delivery slot is reserved.",
"CustomerForename": "James"
}
Scan Item....5000175411118
http://www.techfortesco.com/groceryapi_b1/restservice.aspx?searchtext=
+5000175411118&extendedinfo=N&sessionkey=5VApkMMTjO8LtFCy9VjcSrcZKxoew
+wHGj6XoUUGaH2fBWf73cU&command=PRODUCTSEARCH at /usr/local/share/perl/
+5.14.2/WebService/Tesco/API.pm line 59, <> line 1.
{
"StatusCode": 0,
"StatusInfo": "Command Processed OK",
"PageNumber": 0,
"TotalPageCount": 1,
"TotalProductCount": 1,
"PageProductCount": 1,
"Products":
[
{
"BaseProductId": "50043662",
"EANBarcode": "5000175411118",
"CheaperAlternativeProductId": "",
"HealthierAlternativeProductId": "",
"ImagePath": "http://img.tesco.com/Groceries/pi/118/5000175411118/IDSh
+ot_90x90.jpg",
"MaximumPurchaseQuantity": 99,
"Name": "Oxo 12 Chicken Stock Cubes 71G",
"OfferPromotion": "Price Drop Was Ł1.13 Now Ł1.00 ",
"OfferValidity": "valid from 30/7/2012 until 9/9/2012",
"OfferLabelImagePath": "http://www.tesco.com/Groceries/UIAssets/I/Site
+s/Retail/Superstore/Online/Product/pos/save.png",
"Price": 1,
"PriceDescription": "Ł1.41 each",
"ProductId": "254881114",
"ProductType": "QuantityOnlyProduct",
"UnitPrice": 1.41,
"UnitType": "100g"
}
]
}
malformed JSON string, neither array, object, number, string or atom, 
+at character offset 0 (before "HASH(0x1610440)") at tesc_json1.pl lin
+e 20, <> line 1.
[download]

Clearly I have two (2) errors, despite googling, I am unable figure out what it is I am doing wrong. I would appreciate it if someone could assist.

Thank you - James

Comment on Help with JSON Module Select or Download Code

Replies are listed 'Best First'.
Re: Help with JSON Module by philiprbrenan (Monk) on Sep 07, 2012 at 14:49 UTC
`my $pid = $data->{Products}[0]{ProductId},"\n";` [download] Comma should be dot	[reply] [d/l]
Re^2: Help with JSON Module by foggy3657 (Novice) on Sep 07, 2012 at 15:03 UTC
Thank you, that got rid of one error. Any thoughts on the Malformed JSON error at the bottom? Best wishes - James	[reply]
Re^3: Help with JSON Module by tobyink (Canon) on Sep 07, 2012 at 15:52 UTC
You are passing something which is not a JSON string to JSON's decode method. In particular, I believe you're passing a hashref. `perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'`	[reply]
Re^4: Help with JSON Module by foggy3657 (Novice) on Sep 07, 2012 at 16:09 UTC
Re^5: Help with JSON Module by remiah (Hermit) on Sep 07, 2012 at 22:07 UTC
Some notes below your chosen depth have not been shown here
Re: Help with JSON Module by philiprbrenan (Monk) on Sep 07, 2012 at 15:05 UTC
Please consider taking things step by step so that you build up to the solution incrementally rather than trying to take one giant leap at the start. use feature ":5.14"; use warnings FATAL => qw(all); use strict; use Data::Dump qw(dump pp); use JSON::PP; my $j = JSON::PP->new; my $d = $j->decode(<<'END'); { "StatusCode": 0, "StatusInfo": "Command Processed OK", "BranchNumber": "5528", "CustomerId": "20846164", "CustomerName": "Mr Stubbs", "SessionKey": "5VApkMMTjO8LtFCy9VjcSrcZKxoewwHGj6XoUUGaH2fBWf73cU", "InAmendOrderMode": "N", "BasketID": "98911496", "ChosenDeliverySlotInfo": "No delivery slot is reserved.", "CustomerForename": "James" } END pp($d) [download] Produces: `{ BasketID => 98911496, BranchNumber => 5528, ChosenDeliverySlotInfo => "No delivery slot is reserved.", CustomerForename => "James", CustomerId => 20846164, CustomerName => "Mr Stubbs", InAmendOrderMode => "N", SessionKey => "5VApkMMTjO8LtFCy9VjcSrcZKxoewwHGj6XoUUGaH +2fBWf73cU", StatusCode => 0, StatusInfo => "Command Processed OK", }` [download]	[reply] [d/l] [select]
Re^2: Help with JSON Module by foggy3657 (Novice) on Sep 07, 2012 at 16:04 UTC
Sorry you have lost me. If I add (<<'END'). Then all of the code below changes colour and I'm going to assume it will not run. The last bit of code `my $code = $tesco->product_search({ searchtext => $pn, extendedinfo => + 'N' });` [download] Returns: { "StatusCode": 0, "StatusInfo": "Command Processed OK", "PageNumber": 0, "TotalPageCount": 1, "TotalProductCount": 1, "PageProductCount": 1, "Products": [ { "BaseProductId": "50043662", "EANBarcode": "5000175411118", "CheaperAlternativeProductId": "", "HealthierAlternativeProductId": "", "ImagePath": "http://img.tesco.com/Groceries/pi/118/5000175411118/IDSh +ot_90x90.jpg", "MaximumPurchaseQuantity": 99, "Name": "Oxo 12 Chicken Stock Cubes 71G", "OfferPromotion": "Price Drop Was Ł1.13 Now Ł1.00 ", "OfferValidity": "valid from 30/7/2012 until 9/9/2012", "OfferLabelImagePath": "http://www.tesco.com/Groceries/UIAssets/I/Site +s/Retail/Superstore/Online/Product/pos/save.png", "Price": 1, "PriceDescription": "Ł1.41 each", "ProductId": "254881114", "ProductType": "QuantityOnlyProduct", "UnitPrice": 1.41, "UnitType": "100g" } ] } [download] Apologies if I am appearing to be stupid.	[reply] [d/l] [select]
Re^3: Help with JSON Module by foggy3657 (Novice) on Sep 07, 2012 at 16:25 UTC
This works and returns the correct data "254881114". But I don't see how this helps with my program? #!/usr/bin/perl use feature ":5.14"; use warnings FATAL => qw(all); use strict; use Data::Dump qw(dump pp); use JSON::PP; my $j = JSON::PP->new; my $d = $j->decode(<<'END'); { "StatusCode": 0, "StatusInfo": "Command Processed OK", "PageNumber": 0, "TotalPageCount": 1, "TotalProductCount": 1, "PageProductCount": 1, "Products": [ { "BaseProductId": "50043662", "EANBarcode": "5000175411118", "CheaperAlternativeProductId": "", "HealthierAlternativeProductId": "", "ImagePath": "http://img.tesco.com/Groceries/pi/118/5000175411118/IDSh +ot_90x90.jpg", "MaximumPurchaseQuantity": 99, "Name": "Oxo 12 Chicken Stock Cubes 71G", "OfferPromotion": "Price Drop Was Ł1.13 Now Ł1.00 ", "OfferValidity": "valid from 30/7/2012 until 9/9/2012", "OfferLabelImagePath": "http://www.tesco.com/Groceries/UIAssets/I/Site +s/Retail/Superstore/Online/Product/pos/save.png", "Price": 1, "PriceDescription": "Ł1.41 each", "ProductId": "254881114", "ProductType": "QuantityOnlyProduct", "UnitPrice": 1.41, "UnitType": "100g" } ] } END pp($d); my $pid; $pid = $d->{Products}[0]{ProductId}."\n"; print $pid,"\n"; [download]	[reply] [d/l]
Re: Help with JSON Module by kcott (Archbishop) on Sep 08, 2012 at 06:55 UTC
G'day James, I see ++philiprbrenan has solved the Useless use of a constant ... problem. For the malformed JSON ... problem, it might be better to look at your input JSON rather than what's being output with the error message. Try: `my $code = $tesco->product_search({ searchtext => $pn, extendedinfo => + 'N' }); print $code, "\n"; exit;` [download] You might be able to see the problem by inspection; if not, try running it through the validator you mentioned earlier. [Aside: I'll just point out that chomp is a safer version of chop. Of course, you might have a perfectly valid reason for choosing `chop`.] -- Ken	[reply] [d/l] [select]
Re^2: Help with JSON Module by foggy3657 (Novice) on Sep 08, 2012 at 08:26 UTC
Thank you for trying to help. All your code returns is HASH(0x9fbf738) I have tried the validator and it definitely returns Valid. I can't help thinking that my JSON decode syntax is incorrect somehow. Best wishes - James	[reply]
Re^3: Help with JSON Module by kcott (Archbishop) on Sep 08, 2012 at 08:33 UTC
And there's your problem identified. JSON's decode method has this syntax: `$perl_scalar = $json->decode($json_text)` [download] but you're invoking it as: `$perl_scalar = $json->decode($hash_reference)` [download] Use Data::Dumper to determine what data the hash reference points to. Perhaps your JSON string is in there somewhere. -- Ken	[reply] [d/l] [select]
Re^4: Help with JSON Module by foggy3657 (Novice) on Sep 08, 2012 at 08:51 UTC
Re^5: Help with JSON Module by Corion (Patriarch) on Sep 08, 2012 at 09:07 UTC
Some notes below your chosen depth have not been shown here