os-run-process.md

title	type	description	num	previous-page	next-page
How to run a process?	section	Starting external subprocesses with OS-Lib	14	os-write-file	os-what-else

{% include markdown.html path="_markdown/install-os-lib.md" %}

Starting an external process

To set up a process, use os.proc, then to actually start it, call():

{% tabs 'touch' %} {% tab 'Scala 2 and 3' %}

val path: os.Path = os.pwd / "output.txt"
println(os.exists(path))
// prints: false
val result: os.CommandResult = os.proc("touch", path).call()
println(result.exitCode)
// prints: 0
println(os.exists(path))
// prints: true

{% endtab %} {% endtabs %}

Note that proc accepts both strings and os.Paths.

Reading the output of a process

(The particular commands in the following examples might not exist on all machines.)

Above we saw that call() returned an os.CommandResult. We can access the result's entire output with out.text(), or as lines with out.lines().

For example, we could use bc to do some math for us:

{% tabs 'bc' %} {% tab 'Scala 2 and 3' %}

val res: os.CommandResult = os.proc("bc", "-e", "2 + 2").call()
val text: String = res.out.text()
println(text.trim.toInt)
// prints: 4

{% endtab %} {% endtabs %}

Or have cal show us a calendar:

{% tabs 'cal' %} {% tab 'Scala 2 and 3' %}

val res: os.CommandResult = os.proc("cal", "-h", "2", "2023").call()
res.out.lines().foreach(println)
// prints:
//   February 2023
// Su Mo Tu We Th Fr Sa
//          1  2  3  4
// ...

{% endtab %} {% endtabs %}

Customizing the process

call() takes various optional arguments, too many to explain individually here. For example, you can set the working directory (cwd = ...), set environment variables (env = ...), or redirect input and output (stdin = ..., stdout = ..., stderr = ...). Find more information about the call method on the README of OS-Lib.