ycat

ycat

Command line processor for YAML/JSON files using Jsonnet

Usage

ycat - command line YAML/JSON processor

USAGE:
    ycat [OPTIONS] [INPUT...]
    ycat [OPTIONS] [PIPELINE...]

OPTIONS:
    -o, --out {json|j|yaml|y}    Set output format
    -h, --help                   Show help and exit

INPUT:
    [FILE...]                    Read values from file(s)
    -y, --yaml [FILE...]         Read YAML values from file(s)
    -j, --json [FILE...]         Read JSON values from file(s)
    -n, --null                   Inject a null value 
    -a, --array                  Merge values to array

PIPELINE:
    [INPUT...] [ENV...] EVAL

ENV:
    -v, --var <VAR>=<CODE>       Bind Jsonnet variable to code
              <VAR>==<VALUE>     Bind Jsonnet variable to a string value
    -i, --import <VAR>=<FILE>    Import file into a local Jsonnet variable
        --input-var <VAR>        Change the name of the input value variable (default x) 
        --max-stack <SIZE>       Jsonnet VM max stack size (default 500)

EVAL:
    <SCRIPT>                     Evaluate a Jsonnet script for each value.
    -x, --exec <SCRIPT>          Same as above regardless of file extension.
    -e, --eval <SNIPPET>         Evaluate a Jsonnet snippet for each value.


If no INPUT is specified, values are read from stdin as YAML.
If FILE is "-" or "" values are read from stdin until EOF.
If FILE has no type option, format is detected from extension:
    .json         -> JSON
    .yaml, .yml   -> YAML
    .jsonnet      -> Jsonnet script
    .*            -> YCAT_FORMAT environment variable or YAML

Default output format is YAML unless YCAT_OUTPUT environment variable is 'json'

Examples

Concatenate files to a single YAML stream (type is selected from extension)

$ ycat foo.yaml bar.yaml baz.json

Concatenate files to single JSON stream (one item per-line)

$ ycat -o j foo.yaml bar.yaml baz.json

Concatenate JSON values from stdin to a single YAML file

$ ycat -j

Concatenate YAML from a.txt, stdin, b.yaml and JSON from a.json,

$ ycat -y a.txt - b.txt -j a.json

Concatenate to YAML array

$ ycat a.json b.yaml -a

Concatenate YAML from a.yaml and b.yaml setting key foo to bar on each top level object

$ ycat a.yaml b.yaml -e 'x+{foo: "bar"}'

Same as above with results merged into a single array

$ ycat a.yaml b.yaml -e 'x+{foo: "bar"}' -a

Add kubernetes namespace foo to all resources without namespace

$ ycat *.yaml -e ' { metadata +: { namespace: "foo" } } + x'

Execute foo.jsonnet file with x local var bound to variables from bar.json, baz.yaml

$ ycat bar.json baz.yaml foo.jsonnet

Process with jq using a pipe

$ ycat -oj a.yaml b.json | jq ... | ycat 

Installation

Download an executable for your platform from github releases.

Alternatively, assuming $GOPATH/bin is in $PATH just

go get github.com/alxarch/ycat/cmd/ycat

Input / Output

YAML input

Multiple YAML values separated by ---\n are processed separately. Value reading stops at ...\n or EOF.

YAML output

Each result value is appended to the output with ---\n separator.

JSON input

Multiple JSON values separated by whitespace are processed separately. Value reading stops at EOF.

JSON output

Each result value is appended into a new line of output.

Jsonnet

Jsonnet is a templating language from google that's really versatile in handling configuration files. Visit their site for more information.

Each value is bound to a local variable named x inside the snippet by default. Use --input-var to change the name.

To use Jsonnet code from a file in the snippet use -i <VAR>=<FILE> and the exported value will be available as a local variable in the snippet.

To run a .jsonnet script just add it as an argument. Variables are the same as the snippet.

Local variables are bound before code in a script or snippet. It's up to the user to avoid conflicts/overrides.

Some experimental (undocumented for now) helper methods are bound to _ local variable. These will be documented once tests are in place and the API is more stable. For now look at ycat.libsonnet file.

Caveats

• YAML comments are not preserved. (This is a shortcoming of gopkg.in/yaml package since there's no access to the AST)
• Only the JSON compatible subset of YAML is supported (the one that makes sense)
• Key order of objects is not preserved if processed with Jsonnet

TODO

• Add support for pretty printed output
• Add support for reading .txt files
• Add support for reading files as base64
• Add support for reading files as hex
• Add support for sorting by JSONPath