Carriage Returns and Line Feeds will ultimately bite you – Some Git Tips

Dev Tips



What’s a Carriage and why is it Returning? Carriage Return Line Feed WHAT DOES IT ALL MEAN!?!

The paper on a typewriter rides horizontally on a carriage. The Carriage Return or CR was a non-printable control character that would reset the typewriter to the beginning of the line of text.

However, a Carriage Return moves the carriage back but doesn’t advance the paper by one line. The carriage moves on the X axes…

And Line Feed or LF is the non-printable control character that turns the Platen (the main rubber cylinder) by one line.

Hence, Carriage Turn and Line Feed. Two actions, and for years, two control characters.

Every operating system seems to encode an EOL (end of line) differently. Operating systems in the late 70s all used CR LF together literally because they were interfacing with typewriters/printers on the daily.

Windows uses CRLF because DOS used CRLF because CP/M used CRLF because history.

Mac OS used CR for years until OS X switched to LF.

Unix used just a single LF over CRLF and has since the beginning, likely because systems like Multics started using just LF around 1965. Saving a single byte EVERY LINE was a huge deal for both storage and transmission.

Fast-forward to 2018 and it’s maybe time for Windows to also switch to just using LF as the EOL character for Text Files.

Why? For starters, Microsoft finally updated Notepad to handle text files that use LF.

BUT

Would such a change be possible? Likely not, it would break the world. Here’s NewLine on .NET Core.

public static String NewLine {
    get {
        Contract.Ensures(Contract.Result() != null);
#if !PLATFORM_UNIX
        return "rn";
#else
        return "n";
#endif // !PLATFORM_UNIX
    }
}

Regardless, if you regularly use Windows and WSL (Linux on Windows) and Linux together, you’ll want to be conscious and aware of CRLF and LF.

I ran into an interesting situation recently. First, let’s review what Git does

You can configure .gitattributes to tell Git how to to treat files, either individually or by extension.

When

git config --global core.autocrlf true

is set, git will automatically convert files quietly so that they are checked out in an OS-specific way. If you’re on Linux and checkout, you’ll get LF, if you’re on Windows you’ll get CRLF.

99% of the time this works great.

Except when you are sharing file systems between Linux and Windows. I use Windows 10 and Ubuntu (via WSL) and keep stuff in /mnt/c/github.

However, if I pull from Windows 10 I get CRLF and if I pull from Linux I can LF so then my shell scripts MAY OR MAY NOT WORK while in Ubuntu.

I’ve chosen to create a .gitattributes file that set both shell scripts and PowerShell scripts to LF. This way those scripts can be used and shared and RUN between systems.

*.sh eol=lf
*.ps1 eol=lf

You’ve got lots of choices. Again 99% of the time autocrlf is the right thing.

From the GitHub docs:

You’ll notice that files are matched–*.c, *.sln, *.png–, separated by a space, then given a setting–text, text eol=crlf, binary. We’ll go over some possible settings below.

  • text=auto
    • Git will handle the files in whatever way it thinks is best. This is a good default option.
  • text eol=crlf
    • Git will always convert line endings to CRLF on checkout. You should use this for files that must keep CRLF endings, even on OSX or Linux.
  • text eol=lf
    • Git will always convert line endings to LF on checkout. You should use this for files that must keep LF endings, even on Windows.
  • binary
    • Git will understand that the files specified are not text, and it should not try to change them. The binary setting is also an alias for -text -diff.

Again, the defaults are probably correct. BUT – if you’re doing weird stuff, sharing files or file systems across operating systems then you should be aware. If you’re having trouble, it’s probably CRLF.

* Typewriter by Matunos used under Creative Commons


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