Handling input confirmations in Linux shell scripting

Question

I'm writing a Linux Shell Script to automate a few things I'm doing on Ubuntu 11.04.

Basically, I'm writing a shell script to install NGINX, MySQL, and PHP, and then configure everything. I know how to do everything via the command-line.

However, I don't know how I'm going to handle the parts where the process asks for user input. For example, certain things I install with apt-get ask you for a confirmation i.e. (Y)es or (N)o.

How exactly would I handle auto-confirmation in the shell script i.e. to automatically confirm Yes or No when asked?

Duplicate? stackoverflow.com/questions/226703/… (hope it helps!) — heltonbiker
– heltonbiker, Commented Sep 14, 2011 at 3:06
@heltonbiker: I'm not trying to get input from the user of the shell script, I'm trying to force/make input wherever my script would usually have prompted me to provide a Yes or No response. — ObiHill
– ObiHill, Commented Sep 14, 2011 at 11:19

wormsparty · Accepted Answer · 2011-09-14 09:57:38Z

21

yes | ./script will answer y for everything.

Otherwise, write a script that prints the answers you want, eg:

 echo N
 echo Y
 echo Y

answered Sep 14, 2011 at 9:57

wormsparty

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4 Comments

ObiHill Over a year ago

Thanks for this option. I'm not sure how exactly I would structure the script to do this though, do you have a code sample?

wormsparty Over a year ago

If you don't want to answer always 'yes', I don't really get your question, since it's completely case-dependant. If you want to answer "yes yes no" to a script, simply: printf "y\ny\nn\n" | ./your_script or write a simple script with seperate lines to print each answer, and then: ./answer_script | ./the_script

ObiHill Over a year ago

Thanks a lot. I guess I have multiple options now just in case I want to answer differently to different prompts. This appears to be the most elegant way to do what I want to do being that I only need to call it once with the script.

Sledge Over a year ago

What would you echo if the prompt asks you for a non-character keystroke e.g. "press enter to continue"?

touffy · Accepted Answer · 2011-09-14 09:56:40Z

3

Usually you can call such interactive programs with an option to automatically answer yes to all questions. For instance, you can call apt-get with -y. From the man page :

-y, --yes, --assume-yes Automatic yes to prompts; assume "yes" as answer to all prompts and run non-interactively.

answered Sep 14, 2011 at 9:56

touffy

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Comments

tripleee · Accepted Answer · 2011-09-14 09:47:46Z

2

For Apt, the correct answer is to "preseed" your debconf database with the correct parameters. If Debconf finds the answer from its database, it won't ask. See also http://www.debian-administration.org/articles/394

answered Sep 14, 2011 at 9:47

tripleee

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1 Comment

tripleee Over a year ago

The link is now quite out of date. More recent documentation exists at e.g. wiki.debian.org/DebianInstaller/Preseed and in Appendix B of the Debian Installer manual but these are not particularly beginner-friendly. thornelabs.net/posts/… looks more approachable, but also somewhat prone to future link rot.

LordDoskias · Accepted Answer · 2011-09-14 10:45:36Z

1

Try Expect it might be what you are looking for.

answered Sep 14, 2011 at 10:45

LordDoskias

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1 Comment

ObiHill Over a year ago

Thanks a lot for this, it looks very interesting. Would I have to know exactly what the prompt is going to be i.e. if the command I run in my shell script is going to do something like "Enter your date of birth:", would I have to write Expect "Enter your date of birth:" exactly as the prompt is going to ask for it?!

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