N=0
    ++N () { N=$[$N+1]; echo $N; }
Modify1 () { ++N >> $1; }
Modify  () { for i in $*; do Modify1 $i; done; }
Commit  () { git commit -a -m $; }

rm -Rfv /tmp/eevgit-test2/
mkdir   /tmp/eevgit-test2/
cd      /tmp/eevgit-test2/

git init
Modify file1; git add file1; Commit A
Modify file1;                Commit B

rm -Rfv /tmp/eevgit-test3/
mkdir   /tmp/eevgit-test3/
cd      /tmp/eevgit-test3/
git clone /tmp/eevgit-test2/ .

Modify file1
Commit C
git push origin master

# Enumerating objects: 5, done.
# Counting objects: 100% (5/5), done.
# Writing objects: 100% (3/3), 239 bytes | 239.00 KiB/s, done.
# Total 3 (delta 0), reused 0 (delta 0), pack-reused 0
# remote: error: refusing to update checked out branch: refs/heads/master        
# remote: error: By default, updating the current branch in a non-bare repository        
# remote: is denied, because it will make the index and work tree inconsistent        
# remote: with what you pushed, and will require 'git reset --hard' to match        
# remote: the work tree to HEAD.        
# remote: 
# remote: You can set the 'receive.denyCurrentBranch' configuration variable        
# remote: to 'ignore' or 'warn' in the remote repository to allow pushing into        
# remote: its current branch; however, this is not recommended unless you        
# remote: arranged to update its work tree to match what you pushed in some        
# remote: other way.        
# remote: 
# remote: To squelch this message and still keep the default behaviour, set        
# remote: 'receive.denyCurrentBranch' configuration variable to 'refuse'.        
# To /tmp/eevgit-test2/
#  ! [remote rejected] master -> master (branch is currently checked out)
# error: failed to push some refs to '/tmp/eevgit-test2/'