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

colordiffcolorsdiff()gitpager

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?

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.

Reading the git sources, I found the following hints

in diff.h:

int use_color;

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

example color output

Best Answer

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).

Related Solutions

Bash – Colored text set up with PS1 and colored output from commands mess each other up

The reason is because you're doing it wrong.

You said that you have an "open" color sequence at the end of your prompt. This is wrong. Colors do not nest. There's no "open" and "close". It's "switch to ..." or "reset to default" (which is actually "switch to 0"). So when ls --color=auto switches color for something when it's done it will issue the sequence to reset to the default. It's not "go back to what it was before".

Set the terminal to use the color of text that you want to be "default" (i.e., palette number 0). Then if you want your prompt a different color set it at the beginning and a reset at the end.

For more information read the Bash Prompt HOWTO Chapter 6. ANSI Escape Sequences: Colours and Cursor Movement documentation.

How to pipe colored diff output to less

diff cannot output colors, you need another program, such as colordiff for that. Colors in the terminal are printed via ANSI escape codes which less does not interpret by default. To get less to correctly show colors, you need the -r, or even better, -R switch:

colordiff -- "$file1" "$file2" | less -R

From man less:

   -R or --RAW-CONTROL-CHARS
          Like -r, but only ANSI  "color"  escape  sequences  are
          output in "raw" form.  Unlike -r, the screen appearance
          is maintained correctly in most  cases.   ANSI  "color"
          escape sequences are sequences of the form:

               ESC [ ... m

          where  the  "..."  is  zero or more color specification
          characters For the purpose of keeping track  of  screen
          appearance,  ANSI color escape sequences are assumed to
          not move the cursor.  You  can  make  less  think  that
          characters  other  than  "m"  can end ANSI color escape
          sequences by setting the environment  variable  LESSAN‐
          SIENDCHARS  to  the  list of characters which can end a
          color escape sequence.  And you  can  make  less  think
          that characters other than the standard ones may appear
          between the ESC and the m by  setting  the  environment
          variable  LESSANSIMIDCHARS  to  the  list of characters
          which can appear.

Alternatively, you can use more which will display colors correctly by default.

If you cannot install external programs, you should be able to get the same output using a more manual approach:

diff a b | 
   perl -lpe 'if(/^</){$_ = "\e[1;31m$_\e[0m"} 
              elsif(/^>/){$_ = "\e[1;34m$_\e[0m"}'

Best Answer

Related Solutions

Bash – Colored text set up with PS1 and colored output from commands mess each other up

How to pipe colored diff output to less

Related Question