https://github.com/mcanlas/bash-monad

A DSL for Bash scripts, in Scala
https://github.com/mcanlas/bash-monad

bash dsl scala unix

Last synced: 7 days ago
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A DSL for Bash scripts, in Scala

• Host: GitHub
• URL: https://github.com/mcanlas/bash-monad
• Owner: mcanlas
• License: mit
• Created: 2022-12-23T01:16:30.000Z (almost 2 years ago)
• Default Branch: main
• Last Pushed: 2024-10-20T22:54:23.000Z (17 days ago)
• Last Synced: 2024-10-21T02:55:37.301Z (17 days ago)
• Topics: bash, dsl, scala, unix
• Language: Scala
• Homepage:
• Size: 80.1 KB
• Stars: 1
• Watchers: 3
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# bash-monad

Exploring Bash script generation with a Scala DSL

## In action

Using a DSL, Bash programs can be encoded as a large, monadic data structure.

```scala

val program =

  for {

    _ <- BashProgram("#!/bin/bash")

    // seperate steps are padded with newlines

    _ <- BashProgram("set -euo pipefail")

    // positional argument extraction

    tuple <- Args

      .string("DEPLOY_REGION")

      .string("PAYLOAD_NAME")

    // downstream commands can statically depend on variables declared earlier

    (deployRegion, payloadName) = tuple

    // bash interpolator allows for proper escaping and inline use of bash variables

    // note that the type of `deployRegion` is not `String`

    _ <- Cmd("echo", bash"""deploying to "$deployRegion" \o/ woohoo!!""")

    // this could be defined externally

    awsLambda = MultiLineCommand("aws", "lambda")

    // pretty printing for subcommand style commands

    _ <- Aws.Lambda("list-tags")

      .opt("foo")

      .opt("payload", payloadName)

      .opt("region", deployRegion)

  } yield ()

val compiled =

  Encoder.encode(program)

println(compiled)

```

When compiled, the above will yield the following Bash script:

```bash

#!/bin/bash

set -euo pipefail

if [ $# -ne 2 ]; then

  echo "Usage: $0  "

  exit 1

fi

DEPLOY_REGION=$1

PAYLOAD_NAME=$2

echo deploying to \"${DEPLOY_REGION}\" \\o/ woohoo\!\!

aws lambda list-tags \

  --foo \

  --payload \

    "$PAYLOAD_NAME" \

  --region \

    "$DEPLOY_REGION"

```

## Elsewhere

A `BashProgram[_]` feels isomorphic to a [`Writer[_]` monad](https://typelevel.org/cats/datatypes/writer.html) whose logging type is `List[String]`