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

Answer 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.