How do I append to a file in Scala?

Question

I would like to write a method similar to the following

def appendFile(fileName: String, line: String) = {
}

But I'm not sure how to flesh out the implementation. Another question on here alludes to Scala 2.9 capabilities but I could not find further details.

Also see the second example for append here: http://stackoverflow.com/a/5218279/243233 — Jus12, Dec 31 '12 at 22:02

score 50 · Accepted Answer · edited Jan 05 '13 at 22:16

50

There is no scala-specific IO implementation at the moment, although I understand one written by Jesse Eichar is in incubation. I'm not sure, to what extent this makes use of the new File (path) API in JDK7. Because of this, for now I would go with the simple Java:

val fw = new FileWriter("test.txt", true)
try {
  fw.write( /* your stuff */)
}
finally fw.close()

edited Jan 05 '13 at 22:16

Nils Schmidt

3,702
6
23
28

answered Jul 29 '11 at 08:53

oxbow_lakes

133,303
56
317
449

Javad · Answer 2 · 2021-11-15T19:48:13.490

19

There is a cleaner way — without using external dependencies:

import scala.tools.nsc.io.File

File("filename").writeAll("hello!") // or appendAll("hello!")

or

import scala.tools.nsc.io.Path

Path("/path/to/file").createFile().appendAll("hello!")

Update (November 2020) These APIs are stable (unlike claims in the comments). They have been around since my original answer in 2015 and they are still present in the latest release.

edited Nov 15 '21 at 19:48

answered May 22 '15 at 05:39

Javad

5,755
4
41
51

2

This isn't public a API, and can be removed at any time, so don't be surprised if your code breaks one day. – Michael Zajac Dec 08 '15 at 19:39
From the library: Note: This library is considered experimental and should not be used unless you know what you are doing. – soote Apr 20 '17 at 21:27
I am just too uncomfortable with not closing the file descriptors. I had a requirement of using io.BufferedSource and was forced to wrap into a Java try{}, to perform the last rites in finally{}. – Zeena Dec 04 '18 at 06:16
1

The scala.tools.nsc package is for *New Scala Compiler* - this library is intended for creating scala plugins. See: https://stackoverflow.com/questions/20149397/is-it-better-to-use-import-scala-reflect-io-file-or-java-io-file-in-scala – Janac Meena Mar 21 '19 at 17:42

score 7 · Answer 3 · answered Jul 29 '11 at 08:03

7

val fw = new FileWriter("test.txt", true) ; 
fw.write("This line appended to file!") ; 
fw.close()

answered Jul 29 '11 at 08:03

Shaunak

17,377
5
53
84

score 1 · Answer 4 · answered Dec 14 '20 at 14:29

os-lib is the best option for Scala filesystem operations like appending to a file.

Here's how to append "hear me moo" to a file:

os.write.append(os.pwd/"whatever"/"file1.txt", "\nhear me moo")

os-lib is the best option for filesystem operations because it provides a unified API for all the common functions and also provides a clean API for paths. The Java APIs for filesystems require you to waste brainpower on low level details and force you to import a lot of code.

Here's a full example that creates a directory, creates a file, and then appends to the file if you'd like to experiment on your local machine:

os.makeDir(os.pwd/"whatever")
os.write(os.pwd/"whatever"/"file1.txt", "hi there")
os.write.append(os.pwd/"whatever"/"file1.txt", "\nhear me moo")

How do I append to a file in Scala?

4 Answers4