Python subprocess.run 不工作但显示已完成

Question

Hello first thanks to everyone who contributes. As a new to python self learner you have all saved me alot of time. Now for my first question ever.

I am attempting to use echo to pass a value to a device, specifically /dev/hddled#. I am attempting to do this in Python using the following script, I understand it is not very clean I am still learning.

import sys
import re
import subprocess

disk1 = '[0:0:0:0]'
disk2 = '[1:0:0:0]'
disk3 = '[2:0:0:0]'
disk4 = '[3:0:0:0]'
disk5 = '[4:0:0:0]'
patterns = ['/dev/sda', '/dev/sdb','/dev/sdc','/dev/sdd','/dev/sde']
drives = []


gettingtext = subprocess.check_output(['lsscsi']) 
mytest = subprocess.check_output(['lsscsi']).decode("utf-8")
print(mytest)
print(type(mytest))
lines = mytest.splitlines()

# f = open("lsscsi.txt", "r")
for line in lines: 
    if disk1 in line:
        searchdsk = re.findall(r'\W/.+',line)
        drives.append('1')
        print(str(drives))
    elif disk2 in line:
        searchdsk = re.findall(r'\W/.+', line)
        drives.append('2')
        print(str(drives))
    elif disk3 in line:
        searchdsk = re.findall(r'\W/.+', line)
        drives.append('3')
        print(str(drives))
    elif disk4 in line:
        searchdsk = re.findall(r'\W/.+', line)
        drives.append('4')
        print(str(drives))
    elif disk5 in line:
        searchdsk = re.findall(r'\W/.+', line)
        drives.append('5')
        print(str(drives))
print("These are the drives: " + str(drives))
print(type(drives))
for disknum in drives:
    stuff = subprocess.run(["/usr/bin/echo", "1",  ">", "/dev/hddled" + disknum], shell=True, text=True, capture_output=True)
    stuff
    print("stdout", stuff.stdout)
    print("stderr", stuff.stderr)
    print(type(disknum))
    print("This is number: " + disknum)
    print("This is the command:" + str(stuff))
# f.close()

When I run this code it seems to work just fine and I am getting back the expected values for the drives list. I am also receiving Completed processes with a returncode=0 and the stdout='\n' which is expected.

This is the command:CompletedProcess(args=['/usr/bin/echo', '1', '>', '/dev/hddled5'], returncode=0, stdout='\n', stderr='')

However it does not appear to be echoing the value to the /dev/device. When running the command in a shell directly it works just fine.

echo 1 > /dev/hddled1

I am not sure where to go next as I have run out of things to try and look up. Any help that anyone can provide would be very appreciated.

Thanks

Answer 1

If you use shell=True , you must only pass a single string argument as the first argument to subprocess.run . When you write:

stuff = subprocess.run(["/usr/bin/echo", "1",  ">", "/dev/hddled" + disknum], shell=True, text=True, capture_output=True)

You are in fact only running /usr/bin/echo . You should write instead:

stuff = subprocess.run("/usr/bin/echo 1 > /dev/hddled" + disknum, shell=True, text=True, capture_output=True)

Although I would suggest a format string instead of string concatention (just because I think it's a little more obvious what's going on):

stuff = subprocess.run(f"/usr/bin/echo 1 > /dev/hddled{disknum}", shell=True, text=True, capture_output=True)

---

Of course, instead of calling out to echo , you could also just do this in Python. Something like this should be equivalent:

with open(f"/dev/hddled{disknum}") as fd:
    fd.write('1\n')