Bat doesn't recognize that its the manpage.

[azizsayfiddin]

I set the MANPAGER environment variable to bat -l man, but it doesn't render the man page as it would if I ran man bat | bat -l man. How can I make it recognize the manpages as manpages

[keith-hall]

Piping a man invocation into something else changes the way man outputs the manpage - it removes formatting basically. i.e. man bat | cat is already different from man bat. Indeed, bat wasn't designed to syntax highlight text which already contains ANSI escape sequences (though a recent change was implemented to cater for this: #2999) or weird use of backspace characters to repeat a character to make it bold typewriter style.
The guide for setting the MANPAGER env var (among others) to remove the odd formatting man applies and thus let bat handle it is in the bat readme: https://github.com/sharkdp/bat?tab=readme-ov-file#man

[tamish-max]

MANPAGER="bat -l man" by itself usually isn’t enough, because man changes its output format depending on whether it thinks it is talking to a pager. When you pipe man foo | bat -l man, you are not getting the same raw stream as MANPAGER=... man foo.

The usual fix is to strip the overstrike/backspace formatting first and let bat render the cleaned text:

export MANPAGER='sh -c "col -bx | bat -l man -p"'

Some setups also use:

export MANROFFOPT='-c'

So the short version is: bat is not failing to “detect manpages”; man is feeding the pager a different format. Use the wrapper from the README (col -bx | bat -l man -p) rather than bat -l man directly.