Hello -
I have my own C program where I also use SGR to produce color just like grep
does. I pulled the grep source (2.21) to see how —color=auto was implemented.
In grep.c, lines 2440-2441, there is the code:
if (color_option == 2)
color_option = isatty (STDOUT_FILENO) && should_colorize ();
The thing about using isatty() is that it doesn’t work for the common case of
piping the output of grep to less. What about using fstat(STDOUT_FILENO)
instead? From testing (where “C” is an C program that outputs color using
SGR), I’ve gotten:
COMMAND Should? isatty ISCHR ISFIFO ISREG
======== ======= ====== ===== ====== =====
C T T T F F
C > file F F F F >>T<<---- The interesting case.
C | less T F F T F
Hence, it would seem that we want to output color except when ISREG on the stat
struct on stdout is T. Wouldn’t this make better logic for —color=auto ?
- Paul
