git bush 使用mongodb的命令，为什么not found？

`$ ls
bsondump.exe mongodump.exe mongoperf.exe mongotop.exe
libeay32.dll mongoexport.exe mongorestore.exe ssleay32.dll
mongo.exe mongofiles.exe mongos.exe*
mongod.exe mongoimport.exe mongos.pdb
mongod.pdb mongooplog.exe mongostat.exe
zongyuan.li@lizongyuan-pc MINGW64 /e/mongodb/bin
$ mongo
bash: mongo: command not found
zongyuan.li@lizongyuan-pc MINGW64 /e/mongodb/bin
$ mongo.exe
bash: mongo.exe: command not found
zongyuan.li@lizongyuan-pc MINGW64 /e/mongodb/bin`
请问这是为什么？