Why do you need ./ (dot-slash) before executable or script name to run it in bash?

問題：

When running scripts in bash, I have to write ./ in the beginning:在 bash 中運行腳本時，我必須在開頭寫./ ：

$ ./manage.py syncdb

If I don't, I get an error message:如果我不這樣做，我會收到一條錯誤消息：

$ manage.py syncdb
-bash: manage.py: command not found

What is the reason for this?這是什麼原因？ I thought .我想. is an alias for current folder, and therefore these two calls should be equivalent.是當前文件夾的別名，因此這兩個調用應該是等效的。

I also don't understand why I don't need ./ when running applications, such as:我也不明白爲什麼我在運行應用程序時不需要./ ，例如：

user:/home/user$ cd /usr/bin
user:/usr/bin$ git

(which runs without ./ ) （沒有./運行）

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解決方案：

參考一： https://en.stackoom.com/question/QZ07
參考二： https://stackoom.com/question/QZ07