Git pager is less, but what is causing the output coloring?

Question

less itself isn't capable of doing syntax highlighting, according to this thread.

However, git diff nicely shows colored output in less, its default pager. When I redirect the output of git diff into a file, no color escape sequences are visible.

Does git diff know where it's being sent, and formats the output accordingly? How would one do that?

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I just noticed that git colors the diff output (e.g. git diff), however, it doesn't know how to syntax highlighting in general. e.g.

git show 415fec6:log.tex

doesn't enable any TeX-like syntax.

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Reading the git sources, I found the following hints

in diff.h:

int use_color;

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I was previously referring to syntax highlighting, but that was not correct. What I mean is output coloring, see e.g.

Answer 1

Git uses isatty() to check whether stdout is a tty: this is used to see if a pager must be used (pager.c) as well as colors (color.c).

Answer 2

Running:

git diff --color=always > output

shows the color escapes.

Damn I found it in git's color.c file:

static int check_auto_color(void)                                           
{                                                                           
  if (color_stdout_is_tty < 0)                                              
    color_stdout_is_tty = isatty(1);                                        
  if (color_stdout_is_tty || (pager_in_use() && pager_use_color)) {         
    char *term = getenv("TERM");                                            
    if (term && strcmp(term, "dumb"))                                       
      return 1;                                                             
  }                                                                         
  return 0;                                                                 
}  

Answer 3

less can support colour with -r --raw-control-chars and -R --RAW-CONTROL-CHARS

You could use Pythons pygmentize to do the highlighting and pipe it in.

To combine it all configure a less filter as described on superuser