pythonshellcommand-line-arguments

Why aren't there quotes in sys.argv when they were used at the command line?

Is this a bug?

#!/usr/bin/env python3.6
# filename: tmp.py
import sys

print(sys.argv)

Invoked:

python tmp.py find . -name '*.py'

Actual output:

['tmp.py', 'find', '.', '-name', '*.py']

Expected output:

['tmp.py', 'find', '.', '-name', "'*.py'"]

Note the lack of quotations within the actual output.

Solution

  • The shell is responsible for breaking down the command it's running into a list of C strings. Those strings are then passed to the program being run.

    In the example:

    python tmp.py find . -name '*.py'

    ...the argument list a correctly-implemented shell will generate for the argv element of the execve syscall would look (in C syntax) like:

    char[][]{ "python", "tmp.py", "find", ".", "-name", "*.py", NULL }

    When Python runs, it doesn't know what the original command was: It has no way of knowing if you typed '*.py' or \*.py or any other thing; it only sees the argument list the shell handed off to the operating system.