Cygwin 中环境变量的配置:
1. To see the current value of a particular
 variable, use "printenv ".
   > printenv HOME

2. ":"-separated paths :为分割符
3. set PATH in BASH Shell as follows:
   > export PATH=.:/home/yap/bin:/bin:/usr/local/bin
4. in TCSH Shell, you would do:
   > setenv PATH=.:/home/yap/bin:/bin:/usr/local/bin
 This says to look first in the current directory ".", then /home/yap/bin,
 then /bin, and finally /usr/local/bin. 

 Better still, since you do not know what the previous value
 of PATH is, it is best to simply append what you want to
 the front or back of the current value of PATH.
 > export PATH=.:/home/yap/bin:`printenv PATH`