Niklas Smedemark-Margulies <niklas...@gmail.com> added the comment:
Thanks very much for getting back to me so quickly, and for identifying the reason for the difference in behavior. Sorry to harp on a relatively small behavior, but it cost me a few hours and it might cause confusion for others as well. It still seems like an oversight that the body of a program invoked by `bash -c` would not be quoted. Consider the following two examples: $ bash -c echo my critical data > file.txt $ cat file.txt $ # My data was lost! Or again in Python: >>> import subprocess >>> res1 = subprocess.run(['echo', 'my', 'critical', 'data', '>', 'file.txt'], >>> shell=True, capture_output=True) >>> res1.returncode 0 >>> exit() $ cat file.txt cat: file.txt: No such file or directory $ # The file is not even created! I know that the subsequent args are stored as bash arguments to the first executable/quoted program, for example: $ bash -c 'echo $0' foo foo or >>> res1 = subprocess.run(['echo $0', 'foo'], shell=True, capture_output=True) >>> res1.stdout b'foo\n' However, it seems strange/wrong to invoke an executable via "bash -c executable arg1 arg2", rather than just "executable arg1 arg2"! In other words, the combination of `shell=True` with a sequence of args appears to behave surprisingly/wrong. --- Here's the only part of the docs I could find that discuss the interaction between `shell=True` and args.: """ The shell argument (which defaults to False) specifies whether to use the shell as the program to execute. If shell is True, it is recommended to pass args as a string rather than as a sequence. """ I think there are ~2 cases here: 1) If there exist use cases for setting `shell=True` and doing "bash -c my_executable arg2 arg3", then the documentation should say something like the following: """ Using `shell=True` invokes the sequence of args via `bash -c`. In this case, the first argument MUST be an executable, and the subsequent arguments will be stored as bash parameters for that executable (`$0`, `$1`, etc). """ 2) The body of the program invoked with `bash -c` should always be quoted. In this case, there should either be a code fix to quote the body, or a `ValueError` when `shell=True` and args is a sequence. How does this sound from your perspective? ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue39692> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
