Sstrhsrtj

Let's say I have a file as below

{

    "fruit": "Apple",

}

I want to remove the comma at the end of the line, if and only if the next line contains "}". So, the output will be :

{

    "fruit": "Apple"

}

However, if the file is as below. I do not want to do any change. Since the ,s are not followed by a }

{

    "fruit": "Apple",

    "size": "Large",

    "color": "Red"

}

Anything with sed would be fantastic.

sed -i.bak ':begin;$!N;s/,n}/n}/g;tbegin;P;D' FILE

sed -i.bak = creates a backup of the original file, then applies changes to the file

':begin;$!N;s/,n}/n}/g;tbegin;P;D' = anything ending with , followed by new line and }. Remove the , on the previous line

FILE = the file you want to make the change to

What makes this a non-trivial problem is that the JSON format does not care about whitespace that does not occur inside keys or data. Therefore,

{ "key": "data" }

is the same as

{ "key":

"data"

}

If you add the possibility of a "broken" JSON file, such as

{ "key":

"data", }

it becomes really difficult to properly parse the document with anything other than a JSON parser that knows how to relax the restrictions of the JSON format when parsing the data.

The Perl JSON module can do that, and also pretty-print the result:

$ cat file.json

{

    "fruit": "Apple",

}

$ perl -MJSON -e '@text=(<>);print to_json(from_json("@text", {relaxed=>1}), {pretty=>1})' file.json

{

   "fruit" : "Apple"

}

Here, we read in the whole text document into the array @text. We then decode this while relaxing the parsing (this enables the JSON document to have commas before } and ] and also to include # comments). We then immediately encode the resulting Perl data structure into JSON again and print it.

Another example:

$ cat file.json

{

    "fruit": "Apple",   # a comment

    "stuff": [1, 2, 3,],

}

$ perl -MJSON -e '@text=(<>);print to_json(from_json("@text", {relaxed=>1}), {pretty=>1})' file.json

{

   "fruit" : "Apple",

   "stuff" : [

      1,

      2,

      3

   ]

}

Without pretty printing:

$ perl -MJSON -e '@text=(<>);print to_json(from_json("@text", {relaxed=>1}))' file.json

{"fruit":"Apple","stuff":[1,2,3]}

(no newline at the end of the output)

For really large documents, you would want to use the module's incremental parsing capability and write a proper script for the conversion.