Line endings when redirecting output to file on windows.

[Steven Schveighoffer]

On 6/3/18 12:24 PM, Bastiaan Veelo wrote:
> On Sunday, 3 June 2018 at 15:42:48 UTC, rikki cattermole wrote:
>> On 04/06/2018 3:24 AM, Bastiaan Veelo wrote:
>>> I need some help understanding where extra '\r' come from when output 
>>> is redirected to file on Windows.
>>>
>>> First, this works correctly:
>>>   rdmd --eval="(\"hello\" ~ newline).toFile(\"out.txt\");"
>>> As expected, out.txt contains "hello\r\n".
>>>
>>> I would expect the following to do the same, but it doesn't:
>>>   rdmd --eval="write(\"hello\" ~ newline);" > out.txt
>>> Now out.txt contains "hello\r\r\n".
>>>
>>> Who is doing the extra conversion here, and how do I stop it?
>>>
>>> Thanks!
>>> Bastiaan.
>>
>> That would be cmd. Not sure you can stop it without piping it after 
>> rdmd to remove the \r.

No, it's not cmd. It's File, or more specifically, FILE * from C.

> 
> Thanks. It is starting to dawn on me that I shouldn't use `newline` and 
> `toFile` to write text files, but rather always use "\n" as line ending 
> and use `write` for both writing to stdout and file.
>   rdmd --eval="File(\"out.txt\", \"w\").write(\"hello\n\");"
> and
>   rdmd --eval="write(\"hello\n\");" > out.txt
> both produce "hello\r\n" on Windows.
> 
> Am I correct, or is there a more idiomatic way of writing strings to 
> text files?
> 

Windows C library has this bizarro mode for FILE * called "text" mode, 
which is the default. In this mode, it scans all output, and anywhere it 
sees a '\n', it replaces it with "\r\n".

the `newline` variable contains "\r\n". So what you have done is, output 
"hello\r\n", and File helpfully replaces that "\n" to "\r\n", giving you 
"\r\r\n".

The correct answer, as you have guessed, is don't use newline :) Just 
use \n. It's portable, and line endings on Windows are less important 
these days.

If you want to turn off text mode, set the mode to binary, as this 
should work (note the "wb" mode):

rdmd --eval="File(\"out.txt\", \"wb\").write(\"hello\" ~ newline);"

Note there is also a rawWrite method, which temporarily turns it into 
binary mode, and will work as well:

rdmd --eval="File(\"out.txt\", \"w\").rawWrite(\"hello\" ~ newline);"

-Steve