Built-in Functions

Fx provides a set of built-in functions that can be used to process JSON data.

len(x)

Returns the length of an array, string, or object.

curl https://fx.wtf/example.json | fx len

uniq(x)

Returns unique values of an array.

curl https://fx.wtf/example.json | fx .tags uniq

sort(x)

Sorts an array.

curl https://fx.wtf/example.json | fx .tags sort

sortBy(fn)(x)

Sorts an array by the function fn.

echo '[1,2,3,4,5]' | fx 'sortBy(x => x % 2 > 0)'

sortBy is curried; it returns a function that can be called.

map(fn)(x)

Maps an array using the function fn. The second argument to fn is the index of the current item.

curl https://fx.wtf/example.json | fx .issues 'map(x => x.title)'

map is curried; it returns a function that can be called.

If x is not an array, fn is applied to x itself. This makes map work on JSON streams, where each value is processed separately:

echo '{"a": 1}{"a": 2}' | fx 'map(x => x.a * 10)'

10
20

To map over the values of an object, use Object.entries:

echo '{"a": [1, 2], "b": [3]}' | fx 'Object.entries(x).map(([k, v]) => [k, v.length])' Object.fromEntries

{
  "a": 2,
  "b": 1
}

walk(fn)(x)

Walks an array or an object using the function fn.

curl https://fx.wtf/example.json | fx 'walk(x => typeof x === "string" ? x.toUpperCase() : x)'

Recursively visits every array item and object value, bottom-up, replacing each with the result of fn. The second argument to fn is the index or the key of the current item.

filter(fn)(x)

Filters an array using the function fn. If x is not an array, returns x when fn(x) is truthy and skips it otherwise, which makes filter work on JSON streams.

curl https://fx.wtf/example.json | fx .issues 'filter(x => x.state === "open")'

groupBy(fn)(x)

Groups an array by the function fn.

curl https://fx.wtf/example.json | fx .issues 'groupBy(x => x.state)'

groupBy is curried; it returns a function that can be used to group an array.

chunk(size)(x)

Chunks an array into smaller arrays of a given size.

echo '[1,2,3,4,5]' | fx 'chunk(2)'

chunk is curried; it returns a function that can be used to chunk an array.

flatten(x)

Flattens an array.

echo '[[1,2],[3,4],[5]]' | fx flatten

reverse(x)

Reverses an array.

echo '[1,2,3,4,5]' | fx reverse

keys(x)

Returns an array of keys of an object.

echo '{"a": 1, "b": 2}' | fx keys

values(x)

Returns an array of values of an object.

echo '{"a": 1, "b": 2}' | fx values

list(x)

Prints an array as a list. This is useful for combining output with other commands.

echo '[1, 2, 3]' | fx list | xargs -I{} echo "The number is {}"

save(x)

Edits the input data in place.

fx example.json 'x.name = x.name.toUpperCase(), x' save

The edited data will be saved to the same example.json file.

The file must be passed as the first argument and contain a single JSON value. save writes to a temporary file and renames it over the original, keeping the file's permissions. It refuses to write through a symbolic link.

toBase64(x)

Encodes a string to base64.

curl https://fx.wtf/example.json | fx .text toBase64

fromBase64(x)

Decodes a base64 string.

echo '"SGVsbG8sIFdvcmxkIQ=="' | fx fromBase64

YAML.stringify(x)

Converts a JSON object to YAML.

curl https://fx.wtf/example.json | fx '.users[]' YAML.stringify

YAML.parse(x)

Converts a YAML string to JSON.

INFO

You can use the --yaml flag to parse YAML:

cat example.yaml | fx --yaml

Fx will also automatically detect YAML files with the .ya?ml extension.

fx example.yaml