fx/docs.md

Documentation

fx can work in two modes: cli and interactive. To start interactive mode pipe into fx any JSON:

$ curl ... | fx

Or you can pass file argument as first parameter:

$ fx my.json

If any argument was passed, fx will apply it and prints to stdout.

Anonymous function

Use an anonymous function as reducer which gets JSON and processes it:

$ echo '{"foo": [{"bar": "value"}]}' | fx 'x => x.foo[0].bar'
value

Binding

If you don't pass anonymous function param => ..., code will be automatically transformed into anonymous function. And you can get access to JSON by this keyword:

$ echo '{"foo": [{"bar": "value"}]}' | fx 'this.foo[0].bar'
value

Dot

It is possible to omit this keyword:

$ echo '{"foo": [{"bar": "value"}]}' | fx .foo[0].bar
value

If single dot is passed, JSON will be processed without modification:

$ echo '{"foo": "bar"}' | fx .
{
  "foo": "bar"
}

Chain

You can pass any number of anonymous functions for reducing JSON:

$ echo '{"foo": [{"bar": "value"}]}' | fx 'x => x.foo' 'this[0]' 'this.bar'
value

Generator

If passed code contains yield keyword, generator expression will be used:

$ curl ... | fx 'for (let user of this) if (user.login.startsWith("a")) yield user'

Access to JSON through this keyword:

$ echo '["a", "b"]' | fx 'yield* this'
[
  "a",
  "b"
]

$ echo '["a", "b"]' | fx 'yield* this; yield "c";'
[
  "a",
  "b",
  "c"
]

Update

You can update existing JSON using spread operator:

$ echo '{"count": 0}' | fx '{...this, count: 1}'
{
  "count": 1
}

Using packages

Use any npm package by installing it globally:

$ npm install -g lodash
$ cat package.json | fx 'require("lodash").keys(this.dependencies)'

Using .fxrc

Create .fxrc file in $HOME directory, and require any packages or define global functions.

For example, access all lodash methods without _ prefix. Put in your .fxrc file:

Object.assign(global, require('lodash/fp'))

And now you will be able to call all lodash methods. For example, see who's been committing to react recently:

curl 'https://api.github.com/repos/facebook/react/commits?per_page=100' \
| fx 'groupBy("commit.author.name")' 'mapValues(size)' toPairs 'sortBy(1)' reverse 'take(10)' fromPairs

To be able require global modules make sure you have correct NODE_PATH env variable.

export NODE_PATH=/usr/local/lib/node_modules

Formatting

If you need something different then JSON (for example arguments for xargs) do not return anything from reducer. undefined value is printed into stderr by default.

echo '[]' | fx 'void 0'
undefined

echo '[1,2,3]' | fx 'this.forEach(x => console.log(x))' 2>/dev/null | xargs echo
1 2 3

Other examples

Convert object to array:

$ cat package.json | fx 'Object.keys(this.dependencies)'
[
  "@medv/prettyjson"
]

By the way, fx has shortcut for Object.keys(this). Previous example can be rewritten as:

$ cat package.json | fx this.dependencies ?

Interactive mode

Click on fields to expand or collapse JSON tree, use mouse wheel to scroll view.

Next commands available in interactive mode:

Key	Command
q or Esc or Ctrl+c	Exit
e/E	Expand/Collapse all
g/G	Goto top/bottom
up/down or k/j	Move cursor up/down
left/right or h/l	Expand/Collapse
.	Edit filter

These commands are available when editing the filter:

Key	Command
Enter	Apply filter
Ctrl+u	Clear filter
Ctrl+w	Delete last part
up/down	Select autocomplete

Selecting text

You may found what you can't just select text in fx. This is due the fact that all mouse events redirected to stdin. To be able select again you need instruct your terminal not to do it. This can be done by holding special keys while selecting:

Key	Terminal
Option+Mouse	iTerm2, Hyper
Fn+Mouse	Terminal.app
Shift+Mouse	Linux