Python subprocess: how to use pipes thrice? [duplicate]

Answer 1

Use subprocess.Popen() with the option shell=True, and you can pass it your entire command as a single string.

Answer 2

def runPipe(cmds):
try: 
    p1 = subprocess.Popen(cmds[0].split(' '), stdin = None, stdout = subprocess.PIPE, stderr = subprocess.PIPE)
    prev = p1
    for cmd in cmds[1:]:
        p = subprocess.Popen(cmd.split(' '), stdin = prev.stdout, stdout = subprocess.PIPE, stderr = subprocess.PIPE)
        prev = p
    stdout, stderr = p.communicate()
    p.wait()
    returncode = p.returncode
except Exception, e:
    stderr = str(e)
    returncode = -1
if returncode == 0:
    return (True, stdout.strip().split('\n'))
else:
    return (False, stderr)

Then execute it like:

runPipe(['ls -1','head -n 2', 'head -n 1'])

Answer 3

Just add a third command following the same example:

p1 = subprocess.Popen(['convert', fileIn, 'bmp:-'], stdout=subprocess.PIPE)
p2 = subprocess.Popen(['mkbitmap', '-f', '2', '-s', '2', '-t', '0.48'], 
     stdin=p1.stdout, stdout=subprocess.PIPE)
p1.stdout.close()
p3 = subprocess.Popen(['potrace', '-t' , '5', '-s' , '-o', fileOut],        
     stdin=p2.stdout,stdout=subprocess.PIPE)
p2.stdout.close()

output = p3.communicate()[0]