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Scripting JSON

Doing a lot of web stuff and fiddling around with CouchDB, I really got to like JSON as versatile format for things. Installing the JSONView extension for firefox really helps with working with JSON in the browser, but what I’ve been missing so far is an easy way to deal with JSON from bash scripts. Fiddling around with the very interesting NodeJS, I came up with a small node js script that makes JSON handling much easier, the JSON command: It reads a JSON object from stdin and feeds it to a javascript function body with “v” and NodeJS’ “sys” as parameters. The return value of the function is written to stdout. If it was a string, it is written as-is, if it is another object it will be pretty-JSONified.

Simple Example

$ curl -s http://localhost:5984/test | json "return v;"
{
 "db_name": "test",
 "doc_count": 0,
 "doc_del_count": 0,
 "update_seq": 0,
 "purge_seq": 0,
 "compact_running": false,
 "disk_size": 79,
 "instance_start_time": "1274021449672284",
 "disk_format_version": 5
}

Use curl to fetch the status of CouchDB database “test” from the local CouchDB node and then just pretty print it by returning the implicit value v.

$ curl -s http://localhost:5984/test | json "return v.disk_size;"
79

Just print the disk_size of CouchDB database “test”. You can use all the modern JavaScript functions v8 offers plus the implicit “sys” object that lets you log stuff to stderr or inspect objects. A little script that I find highly useful:

#!/bin/bash
# Delete all jcouchdb test databases
DBS=$(curl -s http://localhost:5984/_all_dbs | \
json 'return v.filter( function(db) { return db.indexOf("jcouchdb") == 0; }).join("\n");')

for i in $DBS
do
 curl -X DELETE http://localhost:5984/$i
done

Filter the list of database to only contain those that start with “jcouchdb”, then loop over them to delete.

Links:

Update: Added “return v;” as default function. now also supports “-h” and “–help”.

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