How to append text to a file on a new line

Question

Why does the following Groovy code not append the "hello again" on a new line?

f = new File('myfile.txt')
f.append('hello again!\n')

This adds to myfile.txt after the last line but not on a new line. How do I append the text on a new line?

See https://stackoverflow.com/questions/1761051/difference-between-n-and-r — javaPlease42, May 25 '17 at 19:38

score 45 · Accepted Answer · answered May 01 '14 at 15:40

45

You should put the \n first. That way your newline will be written before your text:

f.append('\nhello again!')

answered May 01 '14 at 15:40

Kai Sternad

I try it on groovy console , and I have the same problem! – May 01 '14 at 15:50
Instead of '\n', have you tried using the line separator of your operating system, as per @MidoDev's answer ? – Kai Sternad May 01 '14 at 15:54
can you give example for that ? – May 01 '14 at 15:56
3

f.append(System.getProperty("line.separator")+"hello again!") – Kai Sternad May 01 '14 at 15:58
the line separator is defined in system properties, it's not always "\n" maybe "\r\n" so in this case we your our system separator. – CodeIsLife May 01 '14 at 16:05
I think its not so good because now I run my first groovy script on xp machine and the next time it will be on other diff machine as win 2007 – May 01 '14 at 16:07
Just use the separator, it's always safe to do so, as opposed to \n – Kai Sternad May 01 '14 at 16:10
yes "\r\n" works but I need to run the groovy on other WIN type as WIN 2007 or vista , do you think the seperator will work there as it works on my win xp ???? – May 01 '14 at 16:21
If it works for XP, it will also work for any other Windows version. – Kai Sternad May 01 '14 at 16:52

score 11 · Answer 2 · answered Aug 05 '17 at 05:06

11

Yet another way of doing this. In this case, you don't have to add the newline character manually

File greetingsFile = new File("myfile.txt")
greetingsFile.withWriterAppend{ out ->
    out.println 'hello again!'
}

answered Aug 05 '17 at 05:06

Hafiz Adewuyi

1

it does not append but re-write the entire file – Cyril Deba Oct 23 '18 at 11:35

score 7 · Answer 3 · answered Jan 29 '17 at 06:09

7

Groovy's concise syntax for writing into file:

f << '\n' << 'hello again'

answered Jan 29 '17 at 06:09

Does this use a StringBuilder under the hood? – Andi Jay Aug 13 '18 at 15:11
I think [it should be](http://docs.groovy-lang.org/latest/html/gapi/org/codehaus/groovy/runtime/IOGroovyMethods.html#leftShift(java.lang.Appendable,%20java.lang.Object)) equivalent to series of `f.append(..)` calls like this `f.append('\n'); f.append('hello again');`. So the answer is that some other sort of buffering implemented in `f` is used. – Vasiliy Kevroletin Aug 14 '18 at 00:00

score 6 · Answer 4 · answered May 01 '14 at 15:39

6

You can always get the correct new line character through

System.getProperty("line.separator")

so added it before your text

answered May 01 '14 at 15:39

CodeIsLife

you mean to add the line "System.getProperty("line.separator")" before the line --> f.append('hello again!\n') , ( sorry about the question I am very new in groovy ) – May 01 '14 at 15:55
f.append(System.getProperty("line.separator")" + 'hello again!\n') – CodeIsLife May 01 '14 at 16:03
If you are building a lot of strings, then you should probably do something like: def nl=System.getProperty("line.separator"); After that your code would look like: f.append("${nl}hello again!"). It would allow you to create a short pattern you could use in many output statements. – Bill K Nov 29 '16 at 17:20

4 Answers4