Check if current directory is a Git repository

Copied from the bash completion file, the following is a naive way to do it

# Copyright (C) 2006,2007 Shawn O. Pearce <spearce@spearce.org>
# Conceptually based on gitcompletion (http://gitweb.hawaga.org.uk/).
# Distributed under the GNU General Public License, version 2.0.

if [ -d .git ]; then
  echo .git;
else
  git rev-parse --git-dir 2> /dev/null;
fi;

You could either wrap that in a function or use it in a script.

Condensed into a one line condition suitable for bash and zsh

[ -d .git ] && echo .git || git rev-parse --git-dir > /dev/null 2>&1

Use git rev-parse --git-dir

if git rev-parse --git-dir > /dev/null 2>&1; then
  : # This is a valid git repository (but the current working
    # directory may not be the top level.
    # Check the output of the git rev-parse command if you care)
else
  : # this is not a git repository
fi

edit: git-rev-parse now (as of 1.7.0) supports --show-toplevel, so you could do if test "$(pwd)" = "$(git rev-parse --show-toplevel)" to determine if the current directory is the top-level dir.

Based on @Alex Cory's answer:

[ "$(git rev-parse --is-inside-work-tree 2>/dev/null)" = "true" ]

doesn't contain any redundant operations and works in -e mode.

• As @go2null noted, this will not work in a bare repo. If you want to work with a bare repo for whatever reason, you can just check for git rev-parse succeeding, ignoring its output.
  • I don't consider this a drawback because the above line is indended for scripting, and virtually all git commands are only valid inside a worktree. So for scripting purposes, you're most likely interested in being not just inside a "git repo" but inside a worktree.

Not sure if there is a publicly accessible/documented way to do this (there are some internal git functions which you can use/abuse in the git source itself)

You could do something like;

if ! git ls-files >& /dev/null; then
  echo "not in git"
fi

This answer provides a sample POSIX shell function and a usage example to complement @jabbie's answer.

is_inside_git_repo() {
    git rev-parse --is-inside-work-tree >/dev/null 2>&1
}

git returns errorlevel 0 if it is inside a git repository, else it returns errorlevel 128. (It also returns true or false if it is inside a git repository.)

Usage example

for repo in *; do
    # skip files
    [ -d "$repo" ] || continue
    # run commands in subshell so each loop starts in the current dir
    (
        cd "$repo"
        # skip plain directories
        is_inside_git_repo || continue
        printf '== %s ==\n' "$repo"
        git remote update --prune 'origin' # example command
        # other commands here
    )
done

Why not using exit codes? If a git repository exists in the current directory, then git branch and git tag commands return exit code of 0; otherwise, a non-zero exit code will be returned. This way, you can determine if a git repository exist or not. Simply, you can run:

git tag > /dev/null 2>&1

Advantage: Portable. It works for both bare and non-bare repositories, and in sh, zsh and bash.

Explanation

1. git tag: Getting tags of the repository to determine if exists or not.
2. > /dev/null 2>&1: Preventing from printing anything, including normal and error outputs.

TLDR (^R_e^a_l^l_y^?_!): check-git-repo

As an example, you can create a file named check-git-repo with the following contents, make it executable and run it:

#!/bin/sh

if git tag > /dev/null 2>&1; then
    echo "Repository exists!";
else
    echo "No repository here.";
fi

# check if git repo

if [ $(git rev-parse --is-inside-work-tree) = true ]; then
    echo "yes, is a git repo"
    git pull
else
    echo "no, is not a git repo"
    git clone url --depth 1
fi

if ! [[ $(pwd) = *.git/* || $(pwd) = *.git ]]; then 
  if type -P git >/dev/null; then
    ! git rev-parse --is-inside-work-tree >/dev/null 2>&1 || {
     printf '\n%s\n\n' "GIT repository detected." && git status
    }
  fi
fi

Thank you ivan_pozdeev, Now I have a test if inside the .git directory the code will not run so no errors printed out or false exit status.

The "! [[ $(pwd) = .git/ || $(pwd) = *.git ]]" tests if you're not inside a .git repo then it will run the git command. The builtin type command is use to check if you have git installed or it is within your PATH. see help type

##Current branch
echo $(git branch --show-current 2> /dev/null && echo '')
echo $(git branch --show-current 2> /dev/null)

##OR
GIT_DIR=$(git rev-parse --git-dir 2> /dev/null)

open that directory in terminal in linux or cmd on windows and enter git status which should be enough in 2021 to tell you that youre in a git repo and that you have x number of branches with x number of commits.