import os
import subprocess as sp


def shell(cmd):
    """Run each line of a shell script; raise an exception if any line returns
    a nonzero value.
    """
    pin, pout = os.pipe()
    proc = sp.Popen('/bin/sh', stdin=sp.PIPE)
    for line in cmd.split('\n'):
        line = line.strip()
        if line.startswith('#'):
            print '\033[33m> ' + line + '\033[0m'
        else:
            print '\033[32m> ' + line + '\033[0m'
        if line.startswith('cd '):
            os.chdir(line[3:])
        proc.stdin.write(line + '\n')
        proc.stdin.write('echo $? 1>&%d\n' % pout)
        ret = ""
        while not ret.endswith('\n'):
            ret += os.read(pin, 1)
        ret = int(ret.strip())
        if ret != 0:
            print "Error, bailing out."
            sys.exit(-1)
    proc.stdin.close()
    proc.wait()


def ssh(host, cmd):
    """Run commands on a remote host by ssh.
    """
    proc = sp.Popen(['ssh', host], stdin=sp.PIPE)
    proc.stdin.write(cmd)
    proc.wait()