subprocess实现管道

 # shell
 last | cut -d ' ' -f 1 | sort -u 

 #python
 from subprocess import Popen,PIPE

 p1 = Popen('last',shell=True,stdout=PIPE)

 p2 = Popen('cut -d ' ' -f 1,shell=True,stdin=p1.stdout,stdout=PIPE)

 p3 = Popen('sort -u',shell=True,stdin=p2.stdout,stdout=PIPE)

 >>print p3.stdout.read()