[SOLVED] Replacing line in xml on remote linux unit over ssh

keif · 02-04-2016, 02:13 PM

Hello everyone,

I'm having trouble figuring out how to replace a line of xml in an xml file over ssh, due to all the special characters.

I spent a lot of time just trying to do a simple sed command and escape all the special characters but had no success.

I thought it might be easier to create a local variable and export it like so:

Code:

export OLD='<prop name=\"portSettings\" type=\"String\" value=\"\" /\>'
export NEW='<prop name=\"portSettings\" type=\"String\" value=\"9100\" /\>'
ssh root@10.201.7.102 'bash -s' << EOF
sed -i 's/$OLD/$NEW/g' jpos.xml
EOF

As you can see the only real change that needs to be made is the 9100 value.

When I run this I get the following error:

sed: -e expression #1, char 63: unknown option to `s'

I have tried to escape the 's' and that doesn't seem to work either.

I suppose I can resort to pulling the file, editing it locally and then sending it back. But I know there must be a way to do this by executing a one-liner via ssh. I just can't seem to figure it out. Any help would be greatly appreciated.

thesnow · 02-04-2016, 03:14 PM

Your escaping was a smidge off at the end of the strings (/\ vs \/), and you don't have to use 'bash -s', though it should also work.

Code:

export OLD='<prop name=\"portSettings\" type=\"String\" value=\"\" \/>'
export NEW='<prop name=\"portSettings\" type=\"String\" value=\"9100\" \/>'
ssh user@host << EOF
sed -i 's/$OLD/$NEW/g' jpos.xml
EOF

grail · 02-05-2016, 02:29 AM

I would have gone a slightly different way with your sed:

Code:

sed -i '/portSettings/s/""/"9100"/' jpos.xml

sundialsvcs · 02-05-2016, 06:59 AM

The problem that you face ...

and it is a very, very significant(!) one

... is that you will corrupt the remote XML file and thereby render it inoperable.

A wiser approach would be:

Don't attempt to use sed to update an XML file. Instead, use a "real" programming language that can, using libxml2.so of course, parse the file, change its content, and then rewrite it. (Or, using another tool, safely update it in place.
Use rsync -rsh=ssh to replace the entire file on the remote system.
Use version-control, locally, (e.g. git) to maintain up-to-date copies of present and past "known-good" copies of this file for each remote (on your local system), so that any of them can be restored, anywhere, at will.

keif · 02-09-2016, 10:25 AM

Quote:

Originally Posted by thesnow

Your escaping was a smidge off at the end of the strings (/\ vs \/), and you don't have to use 'bash -s', though it should also work.

Code:

export OLD='<prop name=\"portSettings\" type=\"String\" value=\"\" \/>'
export NEW='<prop name=\"portSettings\" type=\"String\" value=\"9100\" \/>'
ssh user@host << EOF
sed -i 's/$OLD/$NEW/g' jpos.xml
EOF

I ended up doing this:

Code:

ssh root@$i  'bash -s' << EOF
sed -i '/portSettings/s/"9100"/""/' jpos.xml
grep portSettings jpos.xml
EOF

This worked great. Thank you so much.

keif · 02-09-2016, 10:27 AM

Quote:

Originally Posted by sundialsvcs

The problem that you face ...

and it is a very, very significant(!) one

... is that you will corrupt the remote XML file and thereby render it inoperable.

A wiser approach would be:

Don't attempt to use sed to update an XML file. Instead, use a "real" programming language that can, using libxml2.so of course, parse the file, change its content, and then rewrite it. (Or, using another tool, safely update it in place.
Use rsync -rsh=ssh to replace the entire file on the remote system.
Use version-control, locally, (e.g. git) to maintain up-to-date copies of present and past "known-good" copies of this file for each remote (on your local system), so that any of them can be restored, anywhere, at will.

sundialsvcs you are so right. This scenario is a true case to try out Ansible or something like that (I say Ansible because we don't have any Ruby guys on our staff :-)

This is something I have been bringing up in my department. Thank you for your suggestions, they are a great help. Keith