kotlin-process

Functional Kotlin friendly way to create external system processes by leveraging:

• Kotlin coroutines
• the powerful but convoluted ProcessBuilder

Installation

repositories {
    mavenCentral()
}

dependencies {
    // Check the 🔝 maven central badge 🔝 for the latest $kotlinProcessVersion
    implementation("com.github.pgreze:kotlin-process:$kotlinProcessVersion")
}

Or in your kotlin script:

@file:DependsOn("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.6.4")
@file:DependsOn("com.github.pgreze:kotlin-process:$kotlinProcessVersion")

Usage

Launch a script and consume its results

Starts a program and prints its stdout/stderr outputs to the terminal:

import com.github.pgreze.process.process
import kotlinx.coroutines.runBlocking

runBlocking {
    val res = process("echo", "hello world")

    check(res.resultCode == 0)

    // By default process output is displayed in the console.
    check(res.output == emptyList<String>())
}

The next step would probably be to capture the output stream, in order to process some data from our own-made script:

val output = process(
    "./my-script.sh", arg1, arg2,

    // Capture stdout lines to do some operations after
    stdout = Redirect.CAPTURE,

    // Default value: prints to System.err
    stderr = Redirect.PRINT,

).unwrap() // Fails if the resultCode != 0

// TODO: process the output
println("Success:\n${output.joinToString("\n")}")

Notice that if you want to capture both stdout and stderr, there will be no way to differentiate them in the returned output:

val res = process(
    "./long-and-dangerous.sh", arg1, arg2,

    // Both streams will be captured,
    // preserving their orders but mixing them in the given output.
    stdout = Redirect.CAPTURE,
    stderr = Redirect.CAPTURE,

    // Allows to consume line by line without delay the provided output.
    consumer = { line -> TODO("process $line") },
)

println("Script finished with result=${res.resultCode}")
println("stdout+stderr:\n" + res.output.joinToString("\n"))

It's also possible to redirect an output stream to a file, or manually by consuming a Flow instance.

import com.github.pgreze.process.Redirect
import com.github.pgreze.process.process
import java.io.File
import java.util.Collections
import kotlinx.coroutines.flow.toList
import kotlinx.coroutines.runBlocking

val errLines = Collections.synchronizedList(mutableListOf<String>())
val res = process(
    "./my-script.sh", arg1, arg2,

    // You can save the execution result in a file,
    stdout = Redirect.ToFile(File("my-input.txt")),

    // If you want to handle this stream yourself,
    // a Flow<String> instance can be used.
    stderr = Redirect.Consume { flow -> flow.toList(errLines) },
)

The last but not least, you can just silence a stream with Redirect.SILENT 😶

Control the environment

Several other options are available to control the script environment:

import com.github.pgreze.process.InputSource
import java.io.File

val res = process(
    "./my-script.sh",
    
    // Provides the input as a string, similar to:
    // $ echo "hello world" | my-script.sh
    stdin = InputSource.fromString("hello world"),

    // Inject custom environment variables:
    env = mapOf("MY_ENV_VARIABLE" to "42"),

    // Override the working directory:
    directory = File("./a/directory"),
)

There are other ways to provide the process input:

// From a file:
process(
    "./my-script.sh",
    stdin = InputSource.FromFile(File("my-input.txt")),
)

// From an InputStream:
process(
    "./my-script.sh",
    stdin = InputSource.fromInputStream(myInputStream)),
)

// Manually by using the raw OutputStream:
process(
    "./my-script.sh",
    stdin = InputSource.FromStream { out: OutputStream ->
        out.write("hello world\n".toByteArray())
        out.flush()
    },
)

Alternative(s)

1. https://github.com/jakubriegel/kotlin-shell
2. https://github.com/lordcodes/turtle