[colug-432] bash pipe + read?

Rick Hornsby richardjhornsby at gmail.com
Mon Nov 16 10:38:15 EST 2015

I've written a shell script that's meant to be run similar to how you install rvm[1] using curl:

	$ curl http://somehost/myscript.sh <http://somehost/myscript.sh> | sudo bash -s devel

It's been working great for a couple of months, but I ran into a problem when I tried to add a read prompt.  Normally, I don't like doing read statements in a shell script.  In this case, I'm using it as a way to allow the user to press enter to skip a timer and reboot the host immediately.  If the user does nothing, the host will reboot after 2 minutes.  I've also trapped SIGINT so they can ctrl-c to cancel the reboot.

I think I understand the problem - what's happening is that because there's an input pipe to bash, read takes the next line of the script as its input instead of taking it from the user - they're both on stdin.  There's what appears to be an answer "Inverting the Fork"[2], but I don't understand the answers.

A simple example[3] showing the difference:

	cat pipe_test.sh | bash

My script is a couple of hundred lines long, and the only part I'm having an issue with is at the very end.  I say that because it's been suggested to contain the entire contents of the script in a HEREDOC - that seems way excessive.

Alternatively, I could make the user do

	$ wget http://somehost/myscript.sh <http://somehost/myscript.sh>; chmod 755 myscript.sh; ./myscript.sh

But that seems far less elegant than curl ... | bash


[1] http://rvm.io <http://rvm.io/>
[2] http://stackoverflow.com/questions/13763942/bash-why-piping-input-to-read-only-works-when-fed-into-while-read-const <http://stackoverflow.com/questions/13763942/bash-why-piping-input-to-read-only-works-when-fed-into-while-read-const>
[3] https://gist.github.com/rjhornsby/dcdaff555d26a00a27b2
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