How to construct json text using string?

Question

I'm trying to construct json text as show below. But the variables such as $token, $state, $failedServers are not been replaced with its value. Note- I don't want to use any module specifically for this to work, I just want some plain string to work. Can anyone help me ?

my $json = '{"serverToken":"$token", "state":"$state","parameters" :"$failedServers"}';

current output was:

{"serverToken":"$token", "state":"$state","parameters" :"$failedServers"}

needed output format:

{"serverToken":"1213", "state":"failed","parameters" :"oracleapps.veeralab.com,suntrust.com"}

Jonathan Hall · Accepted Answer · 2013-11-18 16:23:04Z

4

Your variables are not being replaced, because they are inside of a single-quoted string--that is, they are inside a string quoted by ' characters. This prevents variable substitution.

You will also be much better off creating JSON using a JSON library, such as this one. Simply using a quoted string is very dangerous. Suppose your one of your variables ends up containing a special character; you will end up with invalid JSON.

{"serverToken":"123"ABC", "state":"offline", "paramameters":"bugs"}

If your variables come from user input, really bad things could happen. Imagine that $token is set to equal foo", "state":"online", "foo":"bar. Your resulting JSON structure would be:

{"serverToken":"foo", "state":"online", "foo":"bar", "state":"offline" ...

Certainly not what you want.

Possible solutions:

The most blatantly obvious solution is simply not to the ' quote character. This has the drawback of requiring you to escape your double quote (") characters, though, but it's easy:

my $json = "{\"serverToken\":\"$token\", \"state\":\"$state\",\"parameters\" :\"$failedServers\"}";

Another option is to use sprintf:

my $json = sprintf('{"serverToken":"%s", "state":"%s", "parameters":"%s"}', $token, $state, $failedServers);

But by far, the best solution, because it won't break with wonky input, is to use a library:

use JSON;
my $json = encode_json( {
    serverToken => $token,
    state => $state,
    paramaters => $failedServers
} );

edited Nov 18, 2013 at 16:23

answered Nov 18, 2013 at 16:10

Jonathan Hall

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10 Comments

user1595858 Over a year ago

I don't want to use any library. Can you suggest what I need to correct for it to work?

Jonathan Hall Over a year ago

@user1595858: Yes, don't quote your string using the ' character, as I said in my answer.

Jonathan Hall Over a year ago

@user1595858: Also, why don't you want to use a library? It's the most secure way to do what you need.

Zaid Over a year ago

The backslashes are not the only way out - my $json = qq({"serverToken":"123"ABC",...); works just as well. See perldoc perlop for more.

Jonathan Hall Over a year ago

@Zaid: Indeed, there are other ways, too... they all suck compared to using a proper library :)

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