setting a local bash variable from an ssh command

Question

I am running a chain of sshpass > ssh > commands, I would like to store the exit code of one of those commands ran in the remote server in a variable so I can access it back in the local after ssh is done. What I have done so far does not seem to store anything. Help please!

My Code:

    sshpass -p password ssh user@ip "echo \"first command\" ; su -lc \"./root_script.sh\" ; set MYVAR = $? ; rm root_script.sh \" 
if (( $MYVAR != 0 )) ; then
     echo "Cannot continue program without root password"
     exit
fi

Problem: The commands are all executed (the script runs ok) but the variable MYVAR is not set. I have initialized this to a weird number, and the value does not change. The su exit code is not stored!

Notes:

1) I don't want to do MYVAR=$(ssh....) since ssh is nested within a sshpass, and I don't want the exit code of either of those, I want the return code of the su command ran in the remote server

2) I have used set command because simple assignment gives me an error saying command is not recognized.

3) I have tried different forms of quoting ( \$? or '$?' or "$?" ) but none seem to work

4) I have tried exporting MYVAR to an environment variable, and I have tried unsetting it prior to the line of code. Still no value is stored.

myvar=$(ssh ...) doesn't store the exit code, but rather stores the output. Unless sshpass modifies output, it shouldn't be relevant here. — Charles Duffy
– Charles Duffy, Commented Jul 28, 2014 at 20:14
...beyond that -- export makes a variable accessible to subprocesses. Nothing you can do makes a variable accessible to parent processes without the parent's active involvement (such as reading and storing or eval'ing its child's output stream). — Charles Duffy
– Charles Duffy, Commented Jul 28, 2014 at 20:15
Hence, you could echo $? to return the exit status of the su command. — glenn jackman
– glenn jackman, Commented Jul 28, 2014 at 20:15

Charles Duffy · Accepted Answer · 2014-07-28 20:51:19Z

2

First, you need to put the content you want to capture on stdout of the process.

Second, you need to use single-quotes, not double-quotes, for the remote command -- otherwise, $? will be replaced with its local value before the string is ever passed to ssh!

exit_status=$(sshpass -p password ssh user@ip 'echo "first command" >&2; \
              su -lc "./root_script.sh" >&2; echo "$?"; rm root_script.sh')
echo "Exit status of remote command is $exit_status"

edited Jul 28, 2014 at 20:51

answered Jul 28, 2014 at 20:21

Charles Duffy

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5 Comments

natharra Over a year ago

There is already an echo as a command, giving the user status information. Therefore the first echo will be stored as well into exit_status, wont it?

Charles Duffy Over a year ago

@natharra, indeed; I was assuming you were going to replace it with a real command, but if you actually want to write messages to the user, use >&2 to direct them to stderr.

natharra Over a year ago

Ah, of course. I have to play around a bit with the re-directions since there are some messages I do want the user to see ("password:" and some in the script) but I understand the concept. Thanks!

Charles Duffy Over a year ago

Password prompts are often sent directly to the TTY rather than going through stdout/stderr, but... well, that's a bigger topic.

natharra Over a year ago

it is indeed a bigger topic @CharlesDuffy. I am still having some trouble redirecting things correctly. However, it is a whole new question, mind looking into it?: stackoverflow.com/questions/25018675/…

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