~/project/connection を ~/project/source_file へのシンボリックリンクとして作成するコマンドはどれですか？
~/project/connection
~/project/source_file
readlink ~/project/source_file ~/project/connection
ln ~/project/source_file ~/project/connection
ln -s ~/project/source_file ~/project/connection
ln -s ~/project/connection ~/project/source_file