What does this "python -" do?

Question

I see this command:

curl -sSL https://raw.githubusercontent.com/python-poetry/poetry/master/install-poetry.py | python -

What does this to? What is the "-" called in bash?

It isn't called anything "in bash". As far as `bash` is concerned, it is just a parameter passed to the `python` command. Python interprets as meaning "read the script from standard input". (Read `man python`) — Stephen C, Oct 19 '21 at 14:27
Not to be confused with a Unicode hyphen or dash character (see https://jkorpela.fi/dashes.html) ... which will thoroughly confuse `python` ... and you. — Stephen C, Oct 19 '21 at 14:35

Heinzi · Accepted Answer · 2021-10-19T14:55:46.407

2

This has nothing to do with bash. - has a very specific meaning when passed to the python binary:

-

Read commands from standard input (sys.stdin). [...]

Since, in your example,

curl outputs the downloaded file to stdout and
the shell pipe | passes curl's output to python's stdin,

python will execute the commands contained in the file downloaded by curl.

Note that this is a convention commonly found in various command-line utilities: Providing a single hyphen in place of a file name causes the command to read input from stdin instead of a file.

edited Oct 19 '21 at 14:55

answered Oct 19 '21 at 14:28

Heinzi

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And not just `python`: use of `-` to represent standard input and standard output is a common convention, notably used by many utilities described in the POSIX standard. – chepner Oct 19 '21 at 14:33
Common ... but not universal. – Stephen C Oct 19 '21 at 14:37
@chepner: Indeed, thanks for mentioning that. I have added a note to my answer. – Heinzi Oct 19 '21 at 14:56

What does this "python -" do?

1 Answers1