How to execute a command over ssh and store the value in a variable

Question

I am trying to get the value of uname -r from a remote machine over ssh and use that value in my local script flow.

kern_ver=uname -r
sshpass -p "$passwd" ssh -o StrictHostKeyChecking=no root@$c 'kern_ver=echo \$kern_ver'

But looks like the value is not getting passed back to the local script flow .

Passing variables in remote ssh command, How do I pass a variable from my local server to a remote server?, How to use sshpass?, etc. — jww
– jww, Commented Jun 30, 2019 at 8:35

chepner · Accepted Answer · 2014-08-05 20:55:10Z

7

Storing the command in the variable cmd is optional; you can hard-code the command as a string argument to ssh. The key is that you simply run the command on the remote host via ssh, and capture its output on the local host.

cmd="uname -r"
kern_ver=$(sshpass -p "$passwd" ssh -o StrictHostKeyChecking=no root@"$c" "$cmd")

answered Aug 5, 2014 at 20:55

chepner

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1 Comment

Charles Duffy Over a year ago

"hard-code" is an important point: If the command isn't entirely hardcoded but includes parameterized portions, more complex techniques are required to prevent shell injection attacks.

Charles Duffy · Accepted Answer · 2014-08-05 21:08:20Z

1

Capture is var=$(...), as always.

ssh is a bit interesting because it unconditionally invokes a remote shell, so working with completely arbitrary commands (as opposed to simple things like uname -r) requires a different technique:

filename="/path/to/name with spaces/and/ * wildcard characters *"
printf -v cmd_str '%q ' ls -l "$filename"
output=$(ssh "$host" "$cmd_str")

This way you can use arguments with spaces, and they'll be passed with correct quoting through to the remote system (with the caveat that non-printable characters may be quoted with bash-only syntax, so this is only guaranteed to work in cases where the remote shell is also bash).

answered Aug 5, 2014 at 21:08

Charles Duffy

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