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Convert AWS CloudFormation templates between JSON and YAML formats

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AWS CloudFormation Template Flip

About

AWS CloudFormation Template Flip is a tool that converts AWS CloudFormation templates between JSON and YAML formats, making use of the YAML format's short function syntax where possible.

The term "Flip" is inspired by the well-known Unix command-line tool flip which converts text files between Unix, Mac, and MS-DOS formats.

Installation

AWS CloudFormation Template Flip can be installed using pip:

pip install cfn-flip

Usage

AWS CloudFormation Template Flip is both a command line tool and a python library.

Note that the command line tool is spelled cfn-flip with a hyphen, while the python package is cfn_flip with an underscore.

Command line tool

Usage: cfn-flip [OPTIONS] [INPUT] [OUTPUT]

  AWS CloudFormation Template Flip is a tool that converts AWS
  CloudFormation templates between JSON and YAML formats, making use of the
  YAML format's short function syntax where possible."

Options:
  -i, --input [json|yaml]   Specify the input format. Overrides -j and -y
                            flags.
  -o, --output [json|yaml]  Specify the output format. Overrides -j, -y, and
                            -n flags.
  -j, --json                Convert to JSON. Assume the input is YAML.
  -y, --yaml                Convert to YAML. Assume the input is JSON.
  -c, --clean               Performs some opinionated cleanup on your
                            template.
  -l, --long                Use long-form syntax for functions when converting
                            to YAML.
  -n, --no-flip             Perform other operations but do not flip the
                            output format.
  --version                 Show the version and exit.
  --help                    Show this message and exit.

cfn-flip will detect the format of the input template and convert JSON to YAML and YAML to JSON, respectively.

Examples:

  • Reading from stdin and outputting to stdout:

    cat examples/test.json | cfn-flip
    
  • Reading from a file and outputting to stdout:

    cfn-flip examples/test.yaml
    
  • Reading from a file and outputting to another file:

    cfn-flip examples/test.json output.yaml
    
  • Reading from a file and cleaning up the output

    cfn-flip -c examples/test.json
    

Python package

To use AWS CloudFormation Template Flip from your own python projects, import one of the functions flip, to_yaml, or to_json as needed.

from cfn_flip import flip, to_yaml, to_json

"""
All functions expect a string containing serialised data
and return a string containing serialised data
or raise an exception if there is a problem parsing the input
"""

# flip takes a best guess at the serialisation format
# and returns the opposite, converting json into yaml and vice versa
some_yaml_or_json = flip(some_json_or_yaml)

# to_json expects serialised yaml as input, and returns serialised json
some_json = to_json(some_yaml)

# to_yaml expects serialised json as input, and returns serialised yaml
some_yaml = to_yaml(some_json)

# The clean_up flag performs some opinionated, CloudFormation-specific sanitation of the input
# For example, converting uses of Fn::Join to Fn::Sub
# flip, to_yaml, and to_json all support the clean_up flag
clean_yaml = to_yaml(some_json, clean_up=True)

Configuration paramters

You can configure some parameters like:

max_col_width: Maximum columns before breakline. Default value is 200 To change the configuration you can use:

Environment Variable

Linux/Unix: export CFN_MAX_COL_WIDTH=120

Windows: SET CFN_MAX_COL_WIDTH=120

Python

from cfn_tools._config import config
from cfn_flip import flip, to_yaml, to_json

"""
All functions expect a string containing serialised data
and return a string containing serialised data
or raise an exception if there is a problem parsing the input
"""

# Change the default number of columns to break line to 120
config['max_col_width'] = "120"

# flip takes a best guess at the serialisation format
# and returns the opposite, converting json into yaml and vice versa
some_yaml_or_json = flip(some_json_or_yaml)

# to_json expects serialised yaml as input, and returns serialised json
some_json = to_json(some_yaml)

# to_yaml expects serialised json as input, and returns serialised yaml
some_yaml = to_yaml(some_json)

# The clean_up flag performs some opinionated, CloudFormation-specific sanitation of the input
# For example, converting uses of Fn::Join to Fn::Sub
# flip, to_yaml, and to_json all support the clean_up flag
clean_yaml = to_yaml(some_json, clean_up=True)

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