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UNIX prompt response without Expect script

 

UNIX prompt response without Expect script
gforcing

17 Jun, 2009 - 11:13 AM
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Hello all,

I'm trying to run the following as a UNIX command:

CODE
su username && command


The catch is that it has to be run automatically, so when su prompts for a password, I need a way to fill the password in. I know what the password is, but I can't figure out how to redirect STDIN or STDOUT to give it to the prompt.

Some suggestions have been to write an Expect script, but that's not an option I have available. Any ideas on redirection, for example:

CODE
echo password | su username && command
doesn't work.

Also, I found that

CODE
su username 2>/dev/null
still displays a prompt.

Help!

This post has been edited by gforcing: 17 Jun, 2009 - 11:13 AM

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no2pencil

RE: UNIX Prompt Response Without Expect Script

17 Jun, 2009 - 11:21 AM
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Side stepping the problem, could you setup the user to have su permissions, like in a Wheel group, & that way that user has root level permissions to su to any user.
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gforcing

RE: UNIX Prompt Response Without Expect Script

17 Jun, 2009 - 11:32 AM
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QUOTE(no2pencil @ 17 Jun, 2009 - 11:21 AM) *

Side stepping the problem, could you setup the user to have su permissions, like in a Wheel group, & that way that user has root level permissions to su to any user.


Negative. I also can't setup password-less SSH, or I would have gone that route.
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no2pencil

RE: UNIX Prompt Response Without Expect Script

17 Jun, 2009 - 11:49 AM
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The example that you gave is for the command 'su'.

Are you trying to provide the password to su or ssh?
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gforcing

RE: UNIX Prompt Response Without Expect Script

17 Jun, 2009 - 12:00 PM
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QUOTE(no2pencil @ 17 Jun, 2009 - 11:49 AM) *

The example that you gave is for the command 'su'.

Are you trying to provide the password to su or ssh?


In this case, I'm trying to provide the password to su. I had thought of using SSH as a workaround (because it is possible to set up SSH so that certain accounts don't require a password) but I'm unable to do so.

Here's a more detailed example:

CODE

bob@host$ su jim && whoami
Password: <---- password prompt
jim
bob@host$


What I want to do is this:

CODE

bob@host$ su jim && whoami
jim
bob@host$


with some kind of alteration to the actual command (maybe by redirecting STDIN or STDOUT) to pipe the password in so the prompt doesn't show and the command following && can execute automatically.
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no2pencil

RE: UNIX Prompt Response Without Expect Script

17 Jun, 2009 - 12:07 PM
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From the shell, you can't redirect standard input from the prompt of su (or ssh for that matte, because it's mid execution, & the && is going to wait for the su to finish prior to executing.

If you su to root (or a root level user) you'll find that you can su without being prompted for the password. That can be setup with the wheel account, & that's why I threw that out as a suggestion. I'm sure there is a solution for this, other than using expect, but I'm sure it can't be done from the shell alone.
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martin_mooney27@hotmail.com

RE: UNIX Prompt Response Without Expect Script

30 Jul, 2009 - 01:42 AM
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QUOTE(no2pencil @ 17 Jun, 2009 - 11:21 AM) *

Side stepping the problem, could you setup the user to have su permissions, like in a Wheel group, & that way that user has root level permissions to su to any user.



Only the super user can use su without a password. For security reasons the su command will not allow you specify the password via redirection. It must be typed.

Your best bet is write a program to do what you want and have the set user id bit set on it as well as having the owner as root. I have several bits of code for this but depending on how your environment is managed they may not work for you or may not be allowed.


SSH as suggested before is actually a very good idea.
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