This is a question that I self-answered on my tech blog where I keep the tech-tips which I need to give to myself from time to time, so I decided to move it over here instead. The original blog post is here: http://thehacklist.blogspot.com/2009/04/cygwin-ls-command-not-found.html
If you are a linux enthusiast and really miss those greps and sed/awks on the windows box, you've probably installed cygwin. You tried running it either by double-clicking the cygwin icon on your desktop or the cygwin.bat file in your C:\cygwin directory and got the bash-3.X$ prompt. However, although the pwd or cd commands work, if you try ls, it says:ls: command not found.
- Right click on "My Computer" -> Properties -> Advanced -> Environment Variables
- Add a new environment variable, called CYGWIN_HOME and set its value to C:\cygwin
- Edit the PATH environment variable and add C:\cygwin\bin to it (usually separated by a ';').
- Just click okay, exit any command prompts or bash shells (over cygwin) you may have open, and open it again - it'll work!
Assumption - this assumes that you have installed cygwin at C:\cygwin. If you've kept it someplace else, please modify the above accordingly.
Check the cygwin.bat file, it should have something like:
set PATH=C:\cygwin\bin;C:\cygwin;%PATH%
...etc
bash --login -i
(you don't really need c:\cygwin in there, but I have some additional scripts/bat files there; the key thing is c:\cygwin\bin)
来源：https://stackoverflow.com/questions/14797194/cygwin-ls-command-not-found