Sackmesser - your cli to modify JSON/yaml on the fly

Warning: sackmesser is a prototype at the moment, do not expect the api to be stable

Remember all those times when you had to save JSON in order to find and update a single field? Or worse, where you had to count spaces in yaml? Fear no more, sackmesser will take care of that.

Capabilities

• Supports mutation only, you cannot query JSON with sackmesser
• Input and output formats are disconnected, both yaml and JSON are supported
• Operations: set field, delete field
• Supports multiple operations in one go

Operations

Operations have a signature like op_name(path, args*) where

• path is dot delimited, you could use quotes in case field names contain spaces, dots, commas, etc. For array access you can use array notation:

  echo '{ "a" : { "test prop": 1 } }' | sackmesser mod 'set(a."test prop", "test")'
  {
    "a": {
      "test prop": "test"
    }
  }
  

  echo '{ "a" : { "test prop": [ 1 , true ] } }' | sackmesser mod 'set(a."test prop"[1], "test")'
  "a": {
    "test prop": [
      1,
      "test"
    ]
  }
  

• Zero or more arguments are required for an operation. An argument could be one of

  • a number
  • null
  • A string, you could use single, double quotes and backticks as quotes to minimize escaping
  • A JSON value

Available operations:

Operation	Description
set(path, value)	assign field to a particular value
del(path)	delete a key
merge(path, value)	merge json value into the path. Only JSON values are allowed
pop(path)	remove last element from an array
push(path, value)	add new element to an array

Examples:

If you just want to convert JSON to yaml or back

$ echo '{ "a":1, "prop": { "b": [1,2,3] } }' | sackmesser mod --output-format yaml
a: 1
prop:
    b:
        - 1
        - 2
        - 3

Set a field with a value

$ echo '{ "a":1 }' | sackmesser mod 'set(prop, `{ "test": 123 })`'
{
  "a": 1,
  "prop": "{ \"test\": 123 }"
}

Please note that you can use three types of quotes for strings - double quotes, single quotes, and backticks

$ echo '{ "a":1 }' | sackmesser mod "set(prop, 'value')"
{
  "a": 1,
  "prop": "value"
}

$ echo '{ "a":1 }' | sackmesser mod "set(prop, `value`)"
{
  "a": 1,
  "prop": "value"
}

Set a field with a value that will be parsed as a JSON first

$ echo '{ "a":1 }' | sackmesser mod 'set(prop, { "test": 123 })'
{
    "a": 1,
    "prop": {
        "test": 123
    }
}

You can always spit out a different format if you want!

$ echo '{ "a":1 }' | sackmesser mod --output-format yaml 'set(prop, { "test": 123 })'
{
a: 1
prop:
    test: 123

Merge path with an object

This may come in handy in case you want to apply some specific values to a json template

echo '{ "a" : { "test prop": { "abc": true } } }' | sackmesser mod 'merge(a."test prop", { "testme": true })'
{
  "a": {
    "test prop": {
      "abc": true,
      "testme": true
    }
  }
}

Delete a field

echo '{ "a":1, "deleteme": "please" }' | sackmesser mod 'del(deleteme)'
{
  "a": 1
}

Chain commands

You can supply as many commands as you like if needed

echo '{ "a":1, "deleteme": "please" }' | sackmesser mod 'set(b, "test")' 'del(deleteme)'
{
  "a": 1,
  "b "test",
}

See TODO section for possible changes

Installation

Install Script

Download sackmesser and install it into a local bin directory.

MacOS, Linux, WSL

Latest version:

curl -L https://raw.githubusercontent.com/can3p/sackmesser/master/generated/install.sh | sh

Specific version:

curl -L https://raw.githubusercontent.com/can3p/sackmesser/master/generated/install.sh | sh -s 0.0.4

The script will install the binary into the $HOME/bin folder by default, you can override this by setting $CUSTOM_INSTALL environment variable

Manual Download

Get the archive that fits your system from the Releases page and extract the binary into a folder that is mentioned in your $PATH variable.

Notes

The project has been scaffolded with the help of kleiner

TODO

• More operations
• Some tests will be helpful

Or something like this, suggestions are welcome!

Prior art

There are awesome alternatives to sackmesser, which should be considered as well!

• jq - legendary json processor. Compared to sackmesser has infinite capabilities heavily skewed towards reading the data, however, mutation is also possible, jq works with JSON only
• jj - this tool is optimized for speed and supports JSON lines. Compared to sackmesser it only supports one operation at a time and is optimized for speed

License

See the License