Forcing a python script to take input from STDIN

Question

A python script I need to run takes input only from a file passed as a command line argument, like so:

$ markdown.py input_file

Is there any way to get it to accept input from STDIN instead? I want to be able to do this through Bash, without significantly modifying the python script:

$ echo "Some text here" | markdown.py

If I have to modify the Python script, how would I go about it?

(EDIT: Here is the script that is parsing the command line options.)

Answer 1

Make sure this is near the top of the file:

import sys

Then look for something like this:

filename = sys.argv[1]
f = open(filename)

and replace it with this:

f = sys.stdin

It's hard to be more specific without seeing the script that you're starting with.

Answer 2

I'm not sure how portable it is, but on Unix-y systems you can name /dev/stdin as your file:

$ echo -n hi there | wc /dev/stdin
       0       2       8 /dev/stdin

Answer 3

In the code you have a line like this:

if not len(args) == 1:

What you could do there is to check if you don't have a filename and instead either use "/dev/stdin" (on a system that allows it).

Another solution is to just replace:

if not len(args) == 1:
    parser.print_help()
    return None, None
else:
    input_file = args[0]

with

if not len(args) == 1:
    input_file = sys.stdin
else:
    input_file = open(args[0])

That means of course that the returned "input_file" is no longer a file name but a file object, which means further modifications in the calling function.

First solution is less modifications but more platform specific, second is more work, but should work on more systems.

Answer 4

I'm guessing from the details of your question that you're asking about Python-Markdown, so I tracked down the relevant line in the source code for you: to do it Daniel's way, in line 443 of markdown/__init__.py, you'd want to replace

input_file = codecs.open(input, mode="r", encoding=encoding)

with

input_file = codecs.EncodedFile(sys.stdin, encoding)

Although then you wouldn't be able to actually process files afterwards, so for a more generally useful hack, you could put in a conditional:

if input:
    input_file = codecs.open(input, mode="r", encoding=encoding)
else:
    input_file = codecs.EncodedFile(sys.stdin, encoding)

and then you'd have to adjust markdown/commandline.py to not quit if it isn't given a filename: change lines 72-73

parser.print_help()
return None, None

to

input_file = None

The point is, it's not really a simple thing to do. At this point I was going to suggest using a special file like Mark Rushakoff did, if he hadn't beaten me to it ;-)

Answer 5

I suggest going here:

http://codaset.com/repo/python-markdown/tickets/new

And submitting a ticket requesting them to add the feature. It should be straightforward for them and so they might be willing to go ahead and do it.