Git version control (was: Re: Hello / a 1st question)

[Graham King]

On Thu, 2017-08-10 at 13:40 -0700, H. S. Teoh wrote:
> On Thu, Aug 10, 2017 at 06:40:10PM +0000, Vlad Kudelin wrote:
> >  Lilypond just makes it natural to put everything under
> >    version control! 
> [...]
>
> [...] I use git, which allows me to experiment with different
> branches (different ways of scoring a passage) quickly and easily, and
> without risk of losing previous versions should I decide to revert.
So, here's a bonus, to be inserted immediately below the \version line of your score:

>     \version "2.19.40"
>     
>     % from snippet 197 (more to see at http://lsr.di.unimi.it/LSR/Search ):
>     #(define comml    (object->string (command-line)))
>     #(define loc      (+ (string-rindex comml #\space ) 2)) 
>     #(define commllen (- (string-length comml) 2))
>     #(define filen    (substring comml loc commllen))                   % filename
>     #(define modt     (stat:mtime (stat filen)))                        % Last modified
>     #(define modts    (strftime "%d %b %Y %H:%M:%S" (localtime modt)))  % Command line
>     
>     % gitrev (from http://lilypondblog.org/2014/01/why-use-version-control-for-engraving-scores/#more-2151 )
>     #(use-modules (ice-9 popen))
>     #(use-modules (ice-9 rdelim))
>     
>     % NOTE: This function only reads the first line of the command!
>     #(define (strsystem_internal cmd)
>        (let* ((port (open-input-pipe cmd))
>               (str (read-line port)))
>          (close-pipe port)
>          str))
>     
>     #(define-markup-command (strsystem layout props cmd) (markup?)
>        (interpret-markup layout props
>          (strsystem_internal cmd)))
>     
>     gitrev = \markup { \strsystem "/opt/local/bin/git rev-parse --short HEAD" }
>     
>     \header {
>       tagline = \markup{  \center-column{ 
>             \concat {"Music engraving by Lilypond " 
>                 $(lilypond-version) "-www.lilypond.org"
>             }
>             \line { "Version control for this edition: gitrev " \gitrev " " \modts }
>             }}
>     }

Now you can tell whether that paper copy is up-to-date.  Of course, you don't want this code cluttering up every lilypond score, so best put it in a separate file and \include it.