Project Url: holgerbrandl/kscript
Introduction: Scripting enhancements for Kotlin
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Enhanced scripting support for Kotlin on *nix-based systems.

Kotlin has some built-in support for scripting already but it is not yet feature-rich enough to be a viable alternative in the shell.

In particular this wrapper around kotlinc adds

  • Compiled script caching (using md5 checksums)
  • Dependency declarations using gradle-style resource locators and automatic dependency resolution with maven
  • More options to provide scripts including interpreter mode, reading from stdin, local files or URLs
  • Embedded configuration for Kotlin runtime options
  • Support library to ease the writing of Kotlin scriptlets
  • Deploy scripts as stand-alone binaries

Taken all these features together, kscript provides an easy-to-use, very flexible, and almost zero-overhead solution to write self-contained mini-applications with Kotlin.

kscript presentation from KotlinConf2017!


To use kscript just Kotlin and Maven are required. To install Kotlin we recommend sdkman:

curl -s "https://get.sdkman.io" | bash  # install sdkman
source ~/.bash_profile                  # add sdkman to PATH

sdk install kotlin                      # install Kotlin
sdk install maven                       # install Maven

Once Maven and Kotlin are ready, you can install kscript with

sdk install kscript

To test your installation simply run

kscript --help

kscript can update itself to its latest version by running

kscript --self-update

Installation without sdkman

If you have Kotlin and Maven already and you would like to install the latest kscript release without using sdkman you can do so by unzipping the latest binary release. Don't forget to update your $PATH accordingly.

Installation with Homebrew

On MacOS you can install kscript also with Homebrew

brew install holgerbrandl/tap/kscript

To upgrade to latest version

brew update
brew upgrade holgerbrandl/tap/kscript

Build it yourself

To build kscript yourself, simply clone the repo and do

./gradlew assemble

## Run kscript from output dir

Script Input Modes

The main mode of operation is kscript <script>.

The <script> can be a Kotlin *.kts script file , a script URL, - for stdin, a process substitution file handle, a *.kt source file with a main method, or some kotlin code.

Interpreter Usage

To use kscript as interpreter for a script just point to it in the shebang line of your Kotlin scripts:

#!/usr/bin/env kscript

println("Hello from Kotlin!")
for (arg in args) {
    println("arg: $arg")

Inlined Usage

To use kscript in a workflow without creating an additional script file, you can also use one of its supported modes for inlined usage. The following modes are supported:

  • Directly provide a Kotlin scriptlet as argument
    kscript 'println("hello world")'
  • Pipe a Kotlin snippet into kscript and instruct it to read from stdin by using - as script argument
echo '
println("Hello Kotlin.")
' |  kscript -
  • Using heredoc (preferred solution for inlining) which gives you some more flexibility to also use single quotes in your script:
kscript - <<"EOF"
println("It's a beautiful day!")
  • Since the piped content is considered as a regular script it can also have dependencies ```{bash} kscript - <<"EOF" //DEPS com.offbytwo:docopt: log4j:log4j:1.2.14

import org.docopt.Docopt val docopt = Docopt("Usage: jl [options] []")

println("hello again") EOF

* Finally (for sake of completeness), it also works with process substitution and for sure you can always provide additional arguments (exposed as `args : Array<String>` within the script)
kscript <(echo 'println("k-onliner")') arg1 arg2 arg3

Inlined kscripts are also cached based on md5 checksum, so running the same snippet again will use a cached jar (sitting in ~/.kscript).

URL usage

To support remote scriplet repositories, kscript can also work with URLs. Consider the following hello-world-gist-scriptlet which is hosted on github (but any URL would work). To run it locally as a tool simply refer to it (here using the shortened raw-URL of the script for better readability)

kscript https://git.io/v1cG6 my argu ments

To streamline the usage, the first part could be even aliased:

alias hello_kscript="kscript https://git.io/v1cG6"
hello_kscript my argu ments

Via this mechanism, kscript allows for easy integration of remotely hosted (mini) programs into data workflows.

URL-scripts are cached locally to speed up processing, and kscript --clear-cache can be used to wipe the cache if needed.

See this blogpost for a more extensive overview about URL support in kscript.

Script Configuration

The following directives supported by kscript to configure scripts:

  • //DEPS to declare dependencies with gradle-style locators
  • //KOTLIN_OPTS to configure the kotlin/java runtime environment
  • //INCLUDE to source kotlin files into the script
  • //ENTRY to declare the application entrypoint for kotlin *.kt applications

Declare dependencies with //DEPS

To specify dependencies simply use gradle-style locators. Here's an example using docopt and log4j

#!/usr/bin/env kscript
//DEPS com.offbytwo:docopt:,log4j:log4j:1.2.14

import org.docopt.Docopt
import java.util.*

val usage = """
Use this cool tool to do cool stuff
Usage: cooltool.kts [options] <igenome> <fastq_files>...

 --gtf <gtfFile>     Custom gtf file instead of igenome bundled copy
 --pc-only           Use protein coding genes only for mapping and quantification

val doArgs = Docopt(usage).parse(args.toList())

println("Hello from Kotlin!")
println("Parsed script arguments are: \n" + doArgs)

kscript will read dependencies from all lines in a script that start with //DEPS (if any). Multiple dependencies can be split by comma, space or semicolon.

Configure the runtime with //KOTLIN_OPTS

kscript allows to provide a //KOTLIN_OPTS directive followed by parameters passed on to kotlin similar to how dependencies are defined:

#!/usr/bin/env kscript
//KOTLIN_OPTS -J-Xmx5g  -J-server

println("Hello from Kotlin with 5g of heap memory running in server mode!")

Note: Similar to the runtime you can also tweak the compile step by providing //COMPILER_OPTS.

Ease prototyping with //INCLUDE

kscript supports an //INCLUDE directive to directly include other source files without prior compilation. Absolute and relative paths, as well as URLs are supported. Example:

fun Array<Double>.median(): Double {
    val (lower, upper) = sorted().let { take(size / 2) to takeLast(size / 2) }
    return if (size % 2 == 0) (lower.last() + upper.first()) / 2.0 else upper.first()

Which can be now used using the //INCLUDE directive with

#!/usr/bin/env kscript

//INCLUDE utils.kt

val robustMean = listOf(1.3, 42.3, 7.).median()

The argument can be an URL, absolute or relative file path. Note that URLs used in include directives are cached locally to speed up processing, that is kscript won't fetch URLs again unless the user actively clears the cache with kscript --clear-cache.

For more examples see here.

Use //ENTRY to run applications with main method

kscript also supports running regular Kotlin kt files.

Example: ./examples/Foo.kt:

package examples

//ENTRY examples.Bar

class Bar{
    companion object {
        @JvmStatic fun main(args: Array<String>) {
            println("Foo was called")

fun main(args: Array<String>) = println("main was called")

To run top-level main instead we would use //ENTRY examples.FooKt

The latter is the default for kt files and could be omitted

Annotation driven script configuration

Using annotations instead of comment directives to configure scripts is cleaner and allow for better tooling.

// annotation-driven script configuration

// comment directive
//DEPS de.mpicbg.scicomp:kutils:0.4

To do so kscript supports annotations to be used instead of comment directives:

#!/usr/bin/env kscript

// Declare dependencies
@file:DependsOn("com.beust:klaxon:0.24", "com.github.kittinunf.fuel:fuel:1.3.1")

// To use a custom maven repository you can declare it with
@file:MavenRepository("imagej-releases","http://maven.imagej.net/content/repositories/releases" )

// For compatibility with https://github.com/ligee/kotlin-jupyter kscript supports also
// Note that for compatibility reasons, only one locator argument is allowed for @DependsOnMaven

// Include helper scripts without deployment or prior compilation

// Define kotlin options
@file:CompilerOpts("-jvm-target 1.8")

// declare application entry point (applies on for kt-files)


To enable the use of these annotations in Intellij, the user must add the following artifact (hosted on jcenter) to the project dependencies:


kscript will automatically detect an annotation-driven script, and if so will declare a dependency on this artifact internally.

Note, that if a script is located in a package other than the root package, you need to import the annotations with (e.g. import DependsOn).

Text Processing Mode

kscript can be used as a speedier and more flexible substitute for built-in terminal text tools such as awk or sed. Its text processing mode can be enabled with -t or --text. If so, kscript will

  • Declare com.github.holgerbrandl:kscript-support:1.2.4 as dependency for the script. This support library eases the writing of Kotlin scriptlets for text-processing. It includes solutions to common use-cases like argument parsing, data streaming, IO utilities, and various iterators to streamline the writing of scriptlets for text processing.
  • Import the kscript.* namespace
  • Define variable val lines = kscript.text.StreamUtilKt.resolveArgFile(args) which returns an iterator over the lines in the first input argument of the script, or the standard input if no file arguments are provided to the script

This allows to to replace awkward constructs (or sed orperl) with kotlinesque solutions such as

cat some_file | kscript -t 'lines
    .filter { "^de0[-0]*".toRegex().matches(it) }
    .map { it + "foo:" }

In this example, the extension method Iterable<String>.print() to print the lines to stdout comes from the support API. The rest is stdlib Kotlin.

For more examples using the support library see this blog post.

Treat yourself a REPL with --interactive

To create an interactive kotlin shell (aka REPL) with all script dependencies added to the classpath you can use --interactive.

For example, let's assume the following short script, named CountRecords.kts

#!/usr/bin/env kscript

import de.mpicbg.scicomp.bioinfo.openFasta

if (args.size != 1) {
    System.err.println("Usage: CountRecords <fasta>")

val records = openFasta(java.io.File(args[0]))

To build a REPL that has the declared artifact in its classpath, we can just do

kscript --interactive CountRecords.kts

which will bring up the classpath-enhanced REPL:

Creating REPL from CountRecords.kts
Welcome to Kotlin version 1.1.51 (JRE 1.8.0_151-b12)
>>> import de.mpicbg.scicomp.bioinfo.openFasta

Boostrap IDEA from a kscriptlet

Artifacts and versions will differ between scripts, so it is hard to maintain them all in a single project. To nevertheless provide optimal tooling when scripting with Kotlin kscript allows to create temporary projects for <script> arguments. .

kscript --idea CountRecords.kts

This will open IntelliJ IDEA with a minimalistic project containing just your (1) <script> and (2) a generated gradle.build file:

This assumes that you have the Intellij IDEA command line launcher idea in your PATH. It can be created in IntelliJ under Tools -> Create Command-line Launcher

Deploy scripts as standalone binaries

To deploy a script simply do

kscript --package some_script.kts
./some_script --arg u ments

The created binary will contain a compiled copy of the script, as well as all declared dependencies (fatjar). Also runtime jvm parameters declared via @file:KotlinOpts are used to spin up the JVM.

Just java is required to run these binaries.


Why is kscript not calling the main method in my .kts script?

There is no need for a main method in a Kotlin script. Kotlin *.kts scripts can be more simplistic compared to more common kotlin *.kt source files. The former work without a main method by directly running the provided code from top to bottom. E.g.

print("hello kotlin!")

is a valid Kotlin kts script. Plain and simple, no main, no companion, just a few bits of code.

Does kscript also work for regular kotlin .kt source files with a main as entry point?

Yes, (since v1.6) you can run kotlin source files through kscript. By default it will assume a top-level main method as entry-point.

However in case you're using a companion object to declare the entry point, you need to indicate this via the //ENTRY/@file:Entry directive:

Why does it fail to read my script file when using cygwin?

In order to use cygwin you need to use windows paths to provide your scripts. You can map cygwin paths using cygpath. Example

kscript $(cygpath -w /cygdrive/z/some/path/my_script.kts)

What are performance and resource usage difference between scripting with kotlin and python?

Kotlin is a compiled language, so there is a compilation overhead when you run a script/application written in Kotlin for the first time.

Kotlin runs (mainly) on the JVM which needs some time (~200ms) to start up. In contrast, the python interpreter has close to zero warmup time.

I think there is a consensus that JVM programs execute much faster than python equivalents. Still, python might be faster depending on your specific usecase. Also, with kotlin-native becoming more mature, you could compile into native binaries directly, which should bring it close to C/C++ performance.

Main motivations for using Kotlin over Python for scripting and development are

  • Kotlin is the better designed, more fluent language with much better tooling around it
  • The JVM dependency ecosystem allows for strict versioning. No more messing around with virtualenv, e.g. to run a short 10liner against a specific version of numpy.

Can I use custom artifact repositories?

Yes, via the @MavenRepository annotation. See annotations section or custom_mvn_repo_annot for a complete example


Feel welcome to post ideas and suggestions to our tracker.

More advanced use-cases are documented in the complementary user guide

How to contribute?

We always welcome pull requests and trouble tickets. :-)

Help to spread the word. Great community articles about kscript include

You could also show your support by upvoting kscript here on github, or by voting for issues in Intellij IDEA which impact kscripting. Here are our top 2 tickets/annoyances that we would love to see fixed:

  • KT-11473 Idea does not allow to debug scripts using the builtin debugger
  • KT-13347 Good code is red in injected kotlin language snippets

To allow for more interactive script development, you could also vote/comment on the most annoying REPL issues.

  • KT-12583 IDE REPL should run in project root directory
  • KT-11409 Allow to "Send Selection To Kotlin Console"


The initial version of kscript was kindly contributed by Oscar Gonzalez.

Special thanks to Ilan Pillemer, Andrey Mischenko , Stephen Byrne, Eugene Susla, Eli Hart and oshai for contributing PRs to this repo.

Thanks also to the Scionics Computer Innovation GmbH and the MPI-CBG for supporting this project.

kscript was inspired by kotlin-script which is another great way (now deprecated) to do scripting in Kotlin.

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