In a bash script, use /dev/stdin for first of multiple command line inputs in wrapped script

Question

Let's say I'm writing a bash script myscript.bash, which expects a single argument ($1). One of things it does is call wrapped.py, a python script, which prompts the user for four inputs. I want to submit $1 for the first of these inputs automatically, and then have the user prompted for the rest as normal.

How can I do this? I tried echo $1 | wrapped.py < /dev/stdin, but this submits EOF for the second input requested by wrapped.py, causing a Python EOFError. It does work if I echo -e "$1\na\nb\nc", that is, echo all four inputs...but I want the user to be prompted for the other three. I could write a full-fledged wrapper for the Python script, but that creates maintenance issues, as an update to wrapped.py could e.g. add a fifth question.

Here's what the actual error looks like:

$ echo 'test_app' | django-startproject.py test_app tmp < /dev/stdin
Project name [PROJECT]: Project author [Lincoln Loop]: Traceback (most recent call last):
  File "/usr/local/bin/django-startproject.py", line 7, in <module>
    execfile(__file__)
  File "/home/rich/src/ll-django-startproject/bin/django-startproject.py", line 9, in <module>
    main()
  File "/home/rich/src/ll-django-startproject/bin/django-startproject.py", line 5, in main
    start_project()
  File "/home/rich/src/ll-django-startproject/django_startproject/management.py", line 44, in start_project
    value = raw_input(prompt) or default
EOFError: EOF when reading a line

JB. · Accepted Answer · 2011-02-20 00:05:55Z

1

The easy way:

(echo "$1"; cat) | rest of the pipe here

The disadvantage of this aproach is that the rest of the pipe sees the input as a pipe, and tends to lose most of the nice "interactive" properties. Then again, it depends on your script.

For anything more fancy, you should look into expect.

edited Feb 20, 2011 at 0:05

answered Feb 19, 2011 at 23:57

JB.

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2 Comments

rfrankel Over a year ago

Thanks. That appears to work, except that I don't see the raw_input prompts for inputs 2-4 until I enter values for them, at which point they all print out at once. Is there a workaround for that simpler than using expect?

JB. Over a year ago

Not that I know of. That's a "no", for my personal situation in the world, because if I had to look for/build it, it wouldn't be the simplest anymore.

Ankur Agarwal · Accepted Answer · 2011-02-20 00:18:08Z

0

You can set up things like this:

Your bash script

#!/bin/sh

./test.py $1

And python script

#!/usr/bin/python
import sys
print("In py script now")
for i in sys.argv:
print i

print raw_input('What day is it? ')
print raw_input('What date is it? ')
print raw_input('What month is it? ')

print ("Exiting py script")

And run like this

./myscript.bash abc

Output

In py script now
./test.py
abc
What day is it? 65
65
What date is it? 98
98
What month is it? 14
14
Exiting py script

edited Feb 20, 2011 at 0:18

answered Feb 20, 2011 at 0:10

Ankur Agarwal

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2 Comments

rfrankel Over a year ago

Thanks, but unless I'm missing something, you're not sending $1 to the first raw_input() call, which is what I'm trying to do.

Ankur Agarwal Over a year ago

$1 is available to your .py script. You can use it to assign to any variable there you want.

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