Types of line endings

A line ending is one or two characters used in text files to indicate the end of a line and thus the beginning of the next line.

• Due to historical reasons involving printers, there are two characters involved in newlines on different platforms: line feed (LF) with ASCII code 0x0A and carriage return (CR) with ASCII code 0x0D. In C code, LF is \n and CR is \r. A trick to remembering this is that \r has the r from carriage return.

• There are currently two types of line endings based on the two main operating systems. Linux and Mac OS X systems use the Unix line ending, which is LF. Windows systems use the DOS line ending, which is CR+LF. Classic Mac systems used to use the Mac line ending, which is CR.

• Text files with Unix newlines end up on Windows and files with DOS newlines end up on Linux. I like to use the file tool to check which type of text file I am dealing with:

$ file windows.c
windows.c: C source, ASCII text, with CRLF line terminators

$ file linux.py
linux.py: Python script, ASCII text executable

• The dos2unix tool can be used to convert a file with DOS newlines to Unix newlines in place:

$ dos2unix windows.c

• The unix2dos tool can be used to convert a file with Unix newlines to DOS newlines in place:

$ unix2dos linux.py

• To check and list all the DOS files in a directory:

$ find . -type f | xargs dos2unix -ic

The CR character in DOS files is rendered as ^M at the shell or in Vim, so looking for that character is another way to find DOS files.

• To convert all the DOS files in a directory to Unix, pipe the above list:

$ find . -type f | xargs dos2unix -ic | xargs dos2unix

• To check the type of line ending and convert the file in Vim see this post.