BASH - Assign SSH output to variable

Question

I've read all the threads that I could find regarding this issue that I am having, however I have not yet found a solution to my problem.

First let me say that I am currently attempting to do this work in a very restrictive environment so I do not have the option of messing with configurations or any other admin type functions.

code:

ssh -t username@host "sudo -u user hadoop fs -ls /"

running this returns the output that I am looking for, however the next line will hang and does not assign the output to the variable:

output=$(ssh -t username@host "sudo -u user hadoop fs -ls")

I have attempted any and all variations of this line that I could find. If I do an echo of the variable it just spits out a blank line. The reason for the -t option is becuase without it I was getting an error along the lines of:

sudo: no tty present and no askpass program specified
sudo: pam_authenticate: Conversation error

I really don't have any contingency plans if I can't get this single line to work, so if you can help, it would be greatly appreciated.

Can you build a minimal reproducible example -- ie. come up with a command that other people can run themselves to see the same issue? — Charles Duffy
– Charles Duffy, Commented May 11, 2017 at 17:39
Is it asking you for a password for that remote-root user. Have you tried creating a private key instead of a password? — Louis Loudog Trottier
– Louis Loudog Trottier, Commented May 11, 2017 at 17:40
@LouisLoudogTrottier, ...well -- if it's sudo rather than ssh doing that prompt (or otherwise bailing), then SSH key-level auth won't be of much help. — Charles Duffy
– Charles Duffy, Commented May 11, 2017 at 17:40
It's probably "hanging" because sudo is asking for a password but you don't see the prompt because it is being captured to your variable instead of being displayed. Instead of capturing with $() you could try copying the output to a temp file by adding | tee ~/output on the very end. Then you can read the tmp file after. — ccarton
– ccarton, Commented May 11, 2017 at 17:55
Thanks @ccarton for your explanation! I had started banging my head on my desk since I have been browsing Google for hours trying to get a solution! Then I read your comment and what a relief! Cheers! — Dimitris
– Dimitris, Commented Jun 16, 2018 at 21:49

Rakesh Gupta · Accepted Answer · 2017-05-11 19:41:07Z

1

Please give this a shot. I was able to do it at least 10 times in a row

output=$(sshpass -f <(printf '%s\n' $password) ssh user:@host "sudo ls");
echo $output;

This command is using sshpass to pass the password non interactively to the ssh command.

edited May 11, 2017 at 19:41

answered May 11, 2017 at 18:14

Rakesh Gupta

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Charles Duffy Over a year ago

echo $output is buggy; so is printf '%s\n' $password. Always echo "$output" and printf '%s\n' "$password" -- otherwise a password with spaces would be split onto two separate lines, a file named * READ * ME * NOW * will have the *s replaced with new directory listings, etc. See I just assigned a variable, but echo $variable shows something else!

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