example:
from subprocess import *
proc = Popen(['cat','-'], stdin = PIPE, stdout = PIPE)
msg = 'Through STDIN TO STDOUT'
stdout_value = proc.communicate(msg)[0]
print 'stdout:', stdout_value
output : stdout: Through STDIN TO STDOUT
in this example I have passed the msg string to the called program(cat -) as stdin, what if the called program was the (passwd) command, is it possible to pass two stdin([password value] and [verification password value]) to it ?
Yes, it is possible to pass two lines of input:
msg = 'line1\nline2\n'
Yes and no. Assuming passwd reads from standard input, you would simply write two lines to proc's standard input, either by setting msg to something like mypass\nmypass\n, or simply making two calls to proc.communicate. However, for security reasons passwd reads directly from the terminal, unless you specifically tell it to read from standard input with passwd --stdin (where available).
passwd read from /dev/tty? On my Ubuntu 14.04 LTS system, it reads from stdin.
--stdin option that passwd takes on the Scientific Linux box I'm looking at. It does seem to read from standard input by default, based on the result of passwd < /dev/null.--stdin (and by analogy to sudo or ssh--something reads directly from the terminal, I'm pretty sure). I'm not sure what context requires --stdin.