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pythonpython-3.xsubprocesspopenioerror

Python subprocess.Popen error handling with shell=True/False issues

I am trying to get some error handling for the following code.

In the line subprocess.Popen...... if the shell=True the script will encrypt if a correct file name is given, however there is no file with that name the error code is not printed, but it does show on terminal as no existing file/directory.

if I run the shell=False then I am not able to encrypt files but the error message does print.

Would it be possible for anyone to explain what I am doing wrong? As I have looked at different posts on here but I still do not understand why it won't work. My guess is that it has something to do with the shell=True portion of the script.

SrcDIR ="/home/test/testsource/"

DstDIR ="/home/test/testdest/"

try:
    subprocess.Popen(["openssl aes-128-cbc -salt -in " + SrcDIR + str(var1) + " -out " + DstDIR + "enc." + str() + " -k " + str(var2)], shell=True)
    output3 = ("file " + str(var1) + "created")
    print(output3)
except IOError as reason2:
    errormsg = ("Error encrypting file due to: \n" + str(reason2))
    print(errormsg)
Solution

  • If you set the shell arg to False, then the args argument becomes a sequence of strings, not a single string: the first args element is the name of the program to run, and subsequent elements are the arguments to that program, e.g. (if I understand your code correctly):

    subprocess.Popen \
  (
    [
        "openssl", "aes-128-cbc", "-salt",
        "-in", os.path.join(SrcDIR, var1),
        "-out", os.path.join(DstDIR, "enc." + var1),
        "-k", var2
    ]
  )

    This is also better than trying to pass a single command string with shell = True, because this way you don’t have to beware of characters with special meaning to the shell.