How can I easily determine the last charachter of a file?

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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.");

}