/json-knife

Primary LanguageRust

jk - Json Knife

Development Stage

This project is in its very early stage, a couple of things missing or unstable are

  1. no pretty printing yet
  2. error reporting is weak
  3. query syntax is unstable
  4. action syntax is unstable
  5. and more...

What is it?

Jk is a tool to transform Json data to tabular form, inspired by Micha's json-table, jsawk and Goessner's JsonPath. While Jk's goal is same as json-table's, jk tries to be more intuitive and powerful than json-table. The main difference is that jk adopts a similar form of awk, which makes generating tabular output easier.

How to use?

A jk program consists of three parts:

  <selector> <mode> <action>

where

  • selector is a query string to select interested parts of a Json input, calling it a sub-json
  • mode is how to interpret the selected sub-json
  • action is a list of commands to run over the selected sub-sjon.

Following are some examples with comments after #. First let's print out the json under experiment:

$ cat store.json
{ "store": {                                    
    "book": [                                   
      { "category": "reference",                
        "author": "Nigel Rees",                 
        "title": "Sayings of the Century",      
        "price": 8.95                           
      },                                        
      { "category": "fiction",                  
        "author": "Evelyn Waugh",               
        "title": "Sword of Honour",             
        "price": 12.99                          
      },                                        
      { "category": "fiction",                  
        "author": "Herman Melville",            
        "title": "Moby Dick",                   
        "isbn": "0-553-21311-3",                
        "price": 8.99                           
      },                                        
      { "category": "fiction",                  
        "author": "J. R. R. Tolkien",           
        "title": "The Lord of the Rings",       
        "isbn": "0-395-19395-8",                
        "price": 22.99                          
      }                                         
    ],                                          
    "bicycle": {                                
      "color": "red",                           
      "price": 19.95                            
    }                                           
  }                                             
}

To print first book in Json format

# selector is '.store.book.[0]'
# mode is '@' (ForSelf), meaning just to access current json value
# action is 'p _v', where
#  - 'p' is the command for print
#  - '_v' is the builtin variable for 'current json value'
$ cat store.json | jk ".store.book.[0] @ p _v"
{                                     
  "author": "Nigel Rees",             
  "category": "reference",            
  "price": 8.95,                      
  "title": "Sayings of the Century"   
}

To print authors of each book:

# selector is '.store.book'
# mode is '%' (ForEach), meaning for each array element or object key-value pair
# action is 'p .author' where
#    - 'p' is the command for print
#    - '.author' is the argument to p, which is each  book's author.
$ cat store.json | jk ".store.book % p .author"
Nigel Rees
Evelyn Waugh
Herman Melville
J. R. R. Tolkien

To print all properties for first book

# selector is '.store.book.[0]', which selects the first book
# mode is still 'ForEach'.
# action is to print each key-value. Note '_k' and '_v' are builtin-variables.
$ cat store.json | jk ".store.book.[0] % p _k _v"
author Nigel Rees
category reference
price 8.95
title Sayings of the Century

To print the bicyle color:

# mode is '@', ForSelf, that is not run action over each elements/key-values.
# Instead, action is run over current sub-json itself.
$ cat store.json | jk ".store.bicycle @ p .color"
red

License

MIT