Bash script - connect to remote server and get results

Question

I am trying to write a script that connects to remote server, pings other server (IP as argument) and outputs the result.

So here is what I wrote:

#!/bin/bash
# IP as argument
IP=$1
# Remote connection
ssh -p 22 [email protected]
# Pinging and saving only latency results to RESULT
RESULT=`ping -i 2 -c 4 $IP | grep icmp_seq | awk '{print $7}' | cut -b 6-12`
# Outputs the result    
echo $RESULT

But I am getting an error:

Name or service not known name tester.myserver.com

Of course tester.myserver.com is just example but if I manually type that ssh command with my real remote server address it does work. So I've really no idea why this won't work as a script.

You do know that the ssh command will block until you exit it, and then ping etc. will be executed on the local machine, right? — Biffen
– Biffen, Commented Apr 11, 2016 at 18:16
@Biffen I am total newbie when it comes to writing bash scripts and linux commands. So what would you suggest I do/change in my script? — Cassie Kasandr
– Cassie Kasandr, Commented Apr 11, 2016 at 18:17
The internet is full of examples of how to execute commands over SSH. So I suggest you ask your favourite search engine. — Biffen
– Biffen, Commented Apr 11, 2016 at 18:18
@Biffen as I wrote already in my Q. I know how to execute commands over SSH. I just write ssh... connect to remote server and then execute commands there. Q is how I integrate everything in one bash script and outputs the results. — Cassie Kasandr
– Cassie Kasandr, Commented Apr 11, 2016 at 18:21
The internet is full of examples of how to execute commands over SSH in a script as well. — Biffen
– Biffen, Commented Apr 11, 2016 at 18:22

NiebieskiLuk · Accepted Answer · 2016-04-11 20:32:14Z

3

Change your corresponding line to this:

RESULT=`ssh [email protected] "ping -i 2 -c 4 ${IP}" | grep icmp_seq | awk '{print $7}' | cut -b 6-12`

or without awk:

RESULT=`ssh [email protected] "ping -i 2 -c 4 ${IP} | grep icmp_seq | sed 's/^.*time=\([0-9.]\+\).*/\1/'"`

regards

answered Apr 11, 2016 at 20:32

NiebieskiLuk

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Comments

Community · Accepted Answer · 2017-05-23 12:07:40Z

So the usual way to send a command or list of commands to be executed on a remote server is as follows:

ssh [email protected] "<your commands go here>"

or in your case:

ssh -p 22 [email protected] "ping -i 2 -c 4 $IP | grep icmp_seq | awk '{print \$7}' | cut -b 6-12"

Notice the "\" before $7 to escape the "$". This prevents the $7 to be evaluated to a local variable $7 (which might or not be set) when you run the ssh command, keeping the $7 in the right context with the other commands.

You would still have to set $IP for it to work though, and so all together looks like this:

IP = $1
ssh -p 22 [email protected] "ping -i 2 -c 4 $IP | grep icmp_seq | awk '{print \$7}' | cut -b 6-12"

Now $IP is resolved locally, while $7 is resolved remotely.

I had a similar problem to yours when I tried to connect to a remote server to run some commands and use a local variable - just like you are doing with $IP.

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