[SOLVED] BASH: passing variables through sed via ssh remote command

galron010 · 09-10-2015, 11:11 AM

Hello BASH gurus, I am having issues with inserting variables into a sed command, and then passing that command through SSH. Here is my scenario:

I have a file on multiple different servers. I am trying to create a script on my management server that will log in to each of the remote servers, and edit the file with server-specific information (i.e. IP-address information).

Here is the line I am using in my script

Quote:

ssh $server "sed -i 's/'$nicIP'=.*/'$nicIP'='$newIP'.100/g' file.txt"

In the above example:

$server=root@<server name>
$nicIP=The configuration option in the file to set IP
$newIP=The first 3 octets of the new IP scheme

When the script is executed, and it gets to that portion, the script hangs. I am not sure what to do here. I have tried several variations (removing extra single quotes to leave only 1st and last single quotes, using "s/<old>/<new>/g", etc.), all to no avail.

Any and all possible combinations that might solve this issue will be appreciated.

Thanks.

NevemTeve · 09-10-2015, 11:17 AM

Try to debug:

Code:

REMOTECMD="sed -i 's/'$nicIP'=.*/'$nicIP'='$newIP'.100/g' file.txt"
printf "Now I will try this: %s\n" "$REMOTECMD"
ssh "$server" "$REMOTECMD"

Edit: of course the problem might be in the connecting, so test that too:

Code:

ssh "$server" 'cat /etc/motd'

grail · 09-10-2015, 11:31 AM

As the shell will interpret the variables in the double quotes first I do not think you need all the single quotes:

Code:

ssh $server "sed -i 's/$nicIP=.*/$nicIP=$newIP.100/g' file.txt"

galron010 · 09-10-2015, 01:25 PM

NevemTeve:

Your suggestion for debugging was helpful. It now returns the following:

Quote:

Now I will try this: sed -i 's/nicOption=.*/nicOption=A.B.C.100/g' file.txt
Now I will try this: sed -i 's/nicOption=.*/nicOption=A.B.C.100/g' file.txt
Now I will try this: sed -i 's/nicOption=.*/nicOption=A.B.C.100/g' file.txt
<repeated until ^C is sent>

As you can see, I modified my command slightly, but it now attempts to re-run the command infinitely. When I log into the test server, I see the desired line is changed (and only the desired line is changed, which is of course the desired effect).

It is worth noting that the <ssh $server "sed....."> is in a loop in the script. But that loop is set to run this command, then increment to the next server/next IP in the appropriate arrays, then move past the loop once the script has reached the end of the array. That being the case, I don't think that would be the cause of this loop.

Attempted solutions:

I have tried changing the "/g'" to a "/1g'", and I have tried adding a ";exit" after "file.txt" (a shot in the dark on both. I honestly didn't think either would work)

grail:

Your suggestion was also correct, thank you. Removing the extra single-quotes is, at the very least, extremely helpful in trouble-shooting, as it keeps the code clean.

Anyone have suggestions as to where to go from here?

NevemTeve · 09-10-2015, 11:52 PM

Add command set -xv into your script to see what it is doing

galron010 · 09-11-2015, 11:16 AM

That helped me to discover there was actually a logic error in my loop. Thanks!