On Tuesday, 14 February 2023 at 18:30:05 UTC, seany wrote:
> Hello
>
> Consider the content of a file
>
> ````
> First line \n
> Second line ....
> ....
> data data data data  ... last char
>
> ````
>
> My goal is to find out whether the last character is a new line or not. Please not, it will be sufficient if this works on Linux.
>
> More specifically I want to insert a new line at the end of the file. File.writeline inserts a line at the end of the _newly added line_.
>
> Thus if I had
>
>
> ````
> First line \n
> Second line ....
> ....
> data data data data  ... non-NL-char
>
> ````
>
> and wanted to insert : `newline-word-word-word ... non-NLchar`
>
> Via `file.writeln`, it would end up as
>
> ````
> First line \n
> Second line ....
> ....
> data data data data  ... non-NL-char{no newline or whitespace here}Newline-word-word-word ... non-NLchar{newline}
>
> ````
>
> This is not unexpected. But, I want to make sure, that my appending automatically adds a new line. However, it should not add empty lines.
>
> One brute force method is to copy every line of the file to a temp file or in the RAM and then write back in the original file. I would like to avoid that if possible.
>
> Thanks.

Building on previous response:

module test;
@safe:

import std;

void main()
{
    File myFile =  "somefile.txt";
    myFile.seek(-1, SEEK_END);

    ubyte[1] c;
    () @trusted { myFile.rawRead(c[]); } ();

    if(ControlChar.lf == c[0]) // is this portable??
        writeln("yep, last char is a linefeed.");
    else
        writeln("nope. last char is not a linefeed.");

}