line end Windows versus others

 Windows users that introduce their files in Unix (Linux, Mac) systems sometimes have lots of unexpected problems due to end of line codings. You need to think that a file is just a long stream in which it happens that some hidden characters represent end-of-line. The end of lines is represented with different conventions in the Windows (DOS) and Unix (Linux, Mac) worlds as can be seen here:

https://stackoverflow.com/questions/1552749/difference-between-cr-lf-lf-and-cr-line-break-types

Windows uses CR LF and Unix uses LF. OLd Mac uses CR but modern versions use LF.

How can I see these differences?

- the Windows editor Notepad++ shows them

- the Mac editor Visual Studio Code shows its existence here: 

- vim shows the type when you open the file:

- the file command shows it too

$ file data.txt

data.txt: ASCII text, with CRLF line terminators

$ file extractDescendants.py 

extractDescendants.py: Python script, ASCII text executable

because the last one doesn't say CRLF, then it's LF so it's Unix format.

How can I convert among formats?

Most often you want to convert from Windows (CRLF) to Linux (LF) . 

From memory, Notepad++ allows you to save in Linux format.

In Visual Studio Code, click on the bottom sign "CRLF" and see appear a menu that allows to change it:

In the command line:

many servers have the programs flip and dos2unix that allow to do that:

$ flip -h       

Usage: flip [-t|-u|-d|-m] filename[s]

   Converts ASCII files between Unix, MS-DOS/Windows, or Macintosh newline formats

   Options: 

      -u  =  convert file(s) to Unix newline format (newline)

      -d  =  convert file(s) to MS-DOS/Windows newline format (linefeed + newline)

      -m  =  convert file(s) to Macintosh newline format (linefeed)

      -t  =  display current file type, no file modifications

$ dos2unix -h

dos2unix 6.0.3 (2013-01-25)

Usage: dos2unix [options] [file ...] [-n infile outfile ...]

if you don't have any of this, you can install flip from here:

https://ccrma.stanford.edu/~craig/utility/flip/ 

This is how we compiled it for MacOs:

g++ -ansi -O3 flip.cpp -o flip

You only need to use flip -u myfile and it will modify in-place my file to Unix format. (You DON'T need to use flip -m because that Mac format is obsolete now.) 

For instance:

$ file mydata.txt

mydata.txt: ASCII text, with CRLF line terminators

$ flip -u mydata.txt

$ file mydata.txt

mydata.txt: ASCII text