Perl String Regular Expression - regex

Question

i need some help in Perl regular expressions.
I have this string:
{
"ITEM":[
{
"-itemID": "1000000" ,
"-itemName": "DisneyJuniorLA" ,
"-thumbUrl": "" ,
"-packageID": "1" ,
"-itemPrice": "0" ,
"-isLock": "true"
},
{
"-itemID": "1000001" ,
"-itemName": "31 minutos" ,
"-thumbUrl": "" ,
"-packageID": "1" ,
"-itemPrice": "0" ,
"-isLock": "true"
},
{
"-itemID": "1000002" ,
"-itemName": "Plaza Sésamo" ,
"-thumbUrl": "" ,
"-packageID": "1" ,
"-itemPrice": "0" ,
"-isLock": "true"
},
]
}
The string is in a variable: $jsonString
I have another variable: $itemName
I want to only keep in $jsonString the itemId value that is above itemName (where itemName equals $itemName)
I would really appreciate your help. I am really amateur in regular expressions.
Thank you!

Answer 1

Notwithstanding that your JSON string is very slightly malformed (there's an extra comma after the last element in the array that should be fixed by whoever's generating the "JSON"), attempting to use regexps to handle this just means you now have two problems instead of one.
More specifically, objects within JSON are explicitly unordered sets of key/value pairs. It's perfectly possible that whatever's changing the JSON could be rewritten such that the JSON is semantically identical but serialised differently, making anything that relies on the current structure brittle and error prone.
Instead, use a proper JSON decoder, and then traverse the resulting object hierarchy directly to find the desired element:
use JSON;
use utf8;
# decode the JSON
my $obj = decode_json($jsonString);
# get the ITEM array
my $itemRef = $obj->{ITEM};
# find all elements matching the item name
my #match = grep { $_->{'-itemName'} eq $itemName } #{$itemRef};
# extract the item ID
if (#match) {
my $itemID = $match[0]->{'-itemID'};
print $itemID;
}

Answer 2

Don't use a regular expression to parse JSON. Use JSON.
Basically :
use strict;
use warnings;
use Data::Dumper;
use JSON;
my $json_string;
{
open( my $json_in, "<", 'test.json' );
local $/;
$json_string = <$json_in>;
}
my $json = decode_json ( $json_string );
print Dumper \$json;
foreach my $item ( #{ $json -> {'ITEM'} } ) {
print $item -> {'-itemID'},"\n";
print $item -> {'-itemName'},"\n";
}
But you have to fix your json first. (There's a trailing comma that shouldn't be there. )
JSON is a defined data transfer structure. Whilst you can technically treat it as 'plain text' and extract things from the text, that's definitively the wrong way to do things.
It might work fine for a good long time, but if your source program changes a little - and change their output, whilst still sticking to the JSON standard - your code will break unexpectedly, and you may not realise. That can set off a domino effect of breakages, making a whole system or site just crash and burn. And worse yet - the source of this crash and burn will be hidden away in some script that hasn't been touched in years, so will be very difficult to fix.
This is one of my pet peeves as a professional sysadmin. Please don't even go there.