How to save commands output into a variable via ssh in bash

Question

I want to save an output of a piped sequence of commands into a variable on a remote server. I'm trying to do it via ssh like this:

ssh $host "kernel_ver=`sudo yum list kernel --showduplicates | grep 7.$os_rel | tr -s " " | cut -d" " -f2 | head -n1`; echo $kernel_ver"

I'm getting this errors:

Error: No matching Packages to list
ssh: Could not resolve hostname kernel_ver= ; echo : Name or service not known

$os_rel is a variable in my script containing a number.

I tried different syntax like: "$( )" to capture the output and it still doesn't work.

Stack Overflow is a site for programming and development questions. This question appears to be off-topic because it is not about programming or development. See What topics can I ask about here in the Help Center. Perhaps Super User or Unix & Linux Stack Exchange would be a better place to ask. — jww
– jww, Commented Oct 9, 2017 at 14:28
The question is 100% on topic. Most bash questions are fine. The ones that aren't are purely interactive questions like "how do I change my keybindings?" or "how do I color my prompt?" — John Kugelman
– John Kugelman, Commented Oct 9, 2017 at 15:02

John Kugelman · Accepted Answer · 2017-10-09 13:25:03Z

1

If you use double quotes to surround everything then the backticks will be evaluated by the local shell rather than the remote one. So will the variable reference $kernel_ver. Use single quotes to disable both.

ssh $host 'kernel_ver=`sudo yum list kernel --showduplicates | grep 7.$os_rel | tr -s " " | cut -d" " -f2 | head -n1`; echo $kernel_ver'

If $os_rel is a local variable that you do want expanded then you'll need to temporarily leave single quotes.

ssh $host 'kernel_ver=`sudo yum list kernel --showduplicates | grep 7.'"$os_rel"' | tr -s " " | cut -d" " -f2 | head -n1`; echo $kernel_ver'

answered Oct 9, 2017 at 13:25

John Kugelman

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