ssh : remote command execution doesn't work for modifying env variables

pypieuvre · 02-14-2006, 09:58 AM

Hello,
I m trying to open an ssh connection on a server and immediatly execute a command after bash login.
I set up the rsa authentication to avoid interactive passwords issues.

I'd like to customize the prompt of the shell on the server, WITHOUT modifying anything on it (specially .bashrc or .bash_profile)

I tried

Code:

$> ssh mylogin@myhost "export PS1=\"my prompt\";bash --login"

It works as long as no personal customization is done on targeted account .bashrc : in that case the variable is overwritten ....

Code:

$> ssh mylogin@myhost "bash --login; export PS1=\"my prompt\""

doesn't work at all.

Code:

$> export PS1='my prompt' | ssh mylogin@myhost

doesnt give me any prompt at all

Code:

$> ssh -t ssh mylogin@myhost <<EOF export PS1=my prompt
> EOF

neither

Don't know what to do ... do you have any idea ?
PS: Sorry for my english ...

chrism01 · 02-14-2006, 05:00 PM

What I'd do is create a shell file with your temp alterations and source it befoe executing any other cmds:

ssh mylogin@myhost
old_prompt>. temp_env.sh
new_prompt>

That's a dot followed by a space followed by shell_file name

pypieuvre · 02-15-2006, 04:57 AM

The problem is that I want to do it automatically and without modifying the server's configuration (no script on the server) ...

german · 02-15-2006, 11:29 AM

try this:

Code:

ssh mylogin@myhost "export PS1=\"my prompt\";bash --login --norc"

from the bash man page:

Code:

--norc Do  not  read  and  execute  the system wide initialization file
              /etc/bash.bashrc and the personal initialization file  ~/.bashrc
              if  the  shell  is interactive.  This option is on by default if
              the shell is invoked as sh.

Matir · 02-15-2006, 12:36 PM

Yes... bash --login (without --norc) will always read in configuration files. Specifying the export afterward will set the environment variable when bash EXITS.

chrism01 · 02-15-2006, 04:54 PM

Well, my suggestion would only temporarily alter the env for that run of that ssh call; ie when the process exits, the env goes away and in any case no other process will be affected unless they source the script also.
Normal programming practice.

pypieuvre · 02-16-2006, 02:57 AM

Good points, thanks for the attention guys ;-)

Crism01 I agree with you regarding the way to think about the problem, It's exactly what I'm trying to do, but again your script has to be stored on the server side (no ?), what I'd like to avoid ... and to be run automatically after bash launch.

German , It could be a solution but I don't want to prevent the environmnent to be customized except for specific variables. With your solution the account aliases and variables will be skiped ...

pypieuvre · 02-22-2006, 03:24 AM

No more ideas ?

chrism01 · 02-23-2006, 10:23 PM

I think we need more info on eactly WHAT you are trying to do and WHY....
After all, if you are allowed to login and run stuff on the remote box, you are allowed to add scripts to it... or maybe just manually type in any changes you want???

pypieuvre · 02-24-2006, 09:35 AM

You're right it could be a solution to deploy some configuration files or scripts on the remote box, the problem is that I ve got about 9 000 of them ...

What I m doing is building a centralized gateway, mandatory to access these thousands of servers (to control and grant accesses). You connect to the central gateway, choose the host you want to connect and then your connection is forwarded to the remote server (exactly like you would do directly).

BUT after opening the connection between the gateway and the remote box I would like to modify an environmnent variable 'on the fly' for the bash session...

Am I a little more clear ? I recognize the issue is a bit particular and difficult to realise.

german · 02-24-2006, 09:50 AM

what about a grep of the .bashrc and /etc/bashrc files before running bash? something like (totally untested and my regexp knowledge sucks):

Code:

ssh login@myhost "grep [^PS1] ~/.bashrc | sh; bash --login --norc"

edit: on second thought this absolutely wouldn't work because it uses 2 separate instances of bash.