Thank you for filling out a Git bug report!
Please answer the following questions to help us understand your issue.

What did you do before the bug happened? (Steps to reproduce your issue)
`git grep --no-index 123 /dev/stdin` outside of git repository

What did you expect to happen? (Expected behavior)
Ability to grep input from stdin

What happened instead? (Actual behavior)
`git grep` crashed with SIGABRT

$ git grep --no-index 123 /dev/stdin
BUG: environment.c:215: git environment hasn't been setup
Aborted (core dumped)

What's different between what you expected and what actually happened?
Crash, no grep result

Anything else you want to add:
Plain grep can do that, so I suppose `git grep` could also:

$ echo -e "123\n456\n789" | grep 456 /dev/stdin
456

Please review the rest of the bug report below.
You can delete any lines you don't wish to share.


[System Info]
git version:
git version 2.41.0
cpu: x86_64
no commit associated with this build
sizeof-long: 8
sizeof-size_t: 8
shell-path: /bin/sh
uname: Linux 6.5.6-200.fc38.x86_64 #1 SMP PREEMPT_DYNAMIC Fri Oct  6
19:02:35 UTC 2023 x86_64
compiler info: gnuc: 13.1
libc info: glibc: 2.37
$SHELL (typically, interactive shell): /bin/bash


[Enabled Hooks]
not run from a git repository - no hooks to show