Title: Detect UNIX textfiles
Question: How to detect if an ASCII textfile uses UNIX or Windows linebreaks?
This function will detect if a textfile is a Windows or UNIX textfile, and while we're at it, let's show two versions of the same function, one beautful and one less beautful.
Answer:
First of all, the reason is because Windows uses CRLF ($0D $0A or #13 #10) and UNIX/Linux uses just LF ($0A or #10) as linebreaks in textfiles.
The need to do it is because when using the Readln procedure it will not work on UNIX files because it cannot detect the linebreak. Instead of seeing your application go crazy it might be a nice thing to detect if it's a UNIX file or not in advance, and then provide the option to convert it if necessary.
The way to detect if it's a UNIX or Windows file is to spot the difference, i.e. to see if a CR char precedes the LF char.
Here is a go at it:
function IsFileUNIX(Filename: string): boolean;
var
StopRead: boolean;
F: File of Byte;
CurB, PrevB: Byte;
begin
StopRead := False;
PrevB := 0;
Result := True;
AssignFile(F, Filename);
FileMode := 0; // read only
Reset(F);
while (not Eof(F)) and (StopRead = False) do
begin
Read(F, CurB);
// check if $0D precedes $0A
if CurB = $0A then
begin
Result := PrevB $0D;
StopRead := True;
end;
PrevB := CurB;
end;
end;
Well, this function did what I wanted, however, I thought it looked kind of ugly so I began to think a little bit how I may use the same principle, but execute it with fewer statements and make the function a little bit more beautiful.
Simply replacing the while loop with a repeat loop did miracles, here's the second go at it:
function IsFileUNIX2(Filename: string): boolean;
var
F: File of Byte;
CurB, PrevB: Byte;
begin
AssignFile(F, Filename);
FileMode := 0; // read only
Reset(F);
repeat
PrevB := CurB;
Read(F, CurB);
until (CurB = $0A) or (Eof(F));
// check if $0D precedes $0A
Result := PrevB $0D;
end;
Slightly more beautiful if I may say so myself. :-)
There are other article here on Delphi3000 showing how to actually convert UNIX to Windows textfiles and vice versa.