Determine what line ending is used in a text file

I'd just search the file for the first \r or \n and if it was a \n I'd look at the previous character to see if it's a \r, if so, it's \r\n otherwise it's whichever found.

Notice that text files may have inconsistent line endings. Your program should not choke on that. Using ReadLine on a StreamReader (and similar methods) will take care of any possible line ending automatically.

If you manually read lines from a file, make sure to accept any line endings, even if inconsistent. In practice, this is quite easy using the following algorithm:

• Scan ahead until you find either CR or LF.
• If you read CR, peek ahead at the next character;
• If the next character is LF, consume it (otherwise, put it back).

Here is some advanced guesswork: read the file, count CRs and LFs

if (CR > LF*2) then "Mac" 
else if (LF > CR*2) then "Unix"
else "Windows"

Also note, that newer Macs (Mac OS X) use Unix line endings