Text files on Windows vs. Unix computers have different ways of identifying the end of each line. On Windows computers there are two characters at the end of each line, a Carriage Return (CR) and a Line Feed (LF). On Linux or any Unix type OS, the end is identified by just a Line Feed (LF).
Sometimes you need to convert a text file from one type to the other. Below is one way to do it from the command line on most Unix OSs.
To go from Windows -> Unix
(note: don't use the same file name or it will be empty)
tr -d '\r' < winfile.txt > unixfile.txt
To go from Unix -> Windows.
awk 'sub("$", "\r")' unixfile.txt > winfile.txt