subprocess.run 返回 ValueError：嵌入式 null 字节

Question

Explanation

I try to start a.sh file inside a python3 script with subprocess.run data is the content of a RFID Card with 16 3-digit numbers. I write a Filename to the card-content which is then converted to ASCII format. When reading the card it is converted back to the Filename.

Code

# Check if authenticated
if status == MIFAREReader.MI_OK:
    data = MIFAREReader.MFRC522_Read(8)
    # delete blank spaces
    res = [0 if item == 255 else item for item in data]
    # data is an ASCII code from an RFID card, 
    foldername = "".join(chr(x) for x in res)
    videofile = (str(foldername)+".sh")
    # check if videofile has the correct value/name
    print(videodatei)
    videostart = ("/home/pi/Documents/" +videodatei)
    # check if the complete folder has the correct value
    print(videostart)
    #it is working and returns the exact same value as the working code below
    #this one is working: subprocess.run(['/home/pi/Documents/jonah_aktuell.sh'])

Exception

subprocess.run([videostart])

returns the following error:

Traceback (most recent call last): File "MyRead3.py", line 70, in subprocess.run([videostart]) File "/usr/lib/python3.7/subprocess.py", line 472, in run with Popen(*popenargs, **kwargs) as process: File "/usr/lib/python3.7/subprocess.py", line 775, in init restore_signals, start_new_session) File "/usr/lib/python3.7/subprocess.py", line 1453, in _execute_child restore_signals, start_new_session, preexec_fn) ValueError: embedded null byte

What I have tried

As you can see "videostart" and it's content don't contain a NULL. I also checked, that the variable is a string and made sure with the string() function.

I googled tons of "solutions", but all of the problems contained NULLs somewhere in the variable content, mine doesn't.

I also tried subprocess.call() with the same result.

Answer 1

• chr(0) is a NUL byte.
• UNIX syscalls have their arguments passed as C strings.
• C strings are NUL-terminated -- meaning, they're considered to end at the first NUL byte.

Thus, you cannot pass chr(0) as part of a command-line argument on UNIX, so res = [0 if item == 255 else item for item in data] ensures that foldername = "".join(chr(x) for x in res) will generate a value that cannot be passed in an argument vector if any value contains either 0 or 255.