Bash loop to move directories on a remote host via ssh

Question

I'm trying to figure out a way to perform the following loop on a remote host via ssh.

Basically it renames a series of directories to create a rotating backup. But it's local. I want it to work against directories on a remote host.

while [ $n -gt 0 ];
    do {
    src=$(($n-1))
    dst=$n
    if [ -d /backup/$src ];
    then {
    mv /backup/$src /backup/$dst;
    }
    fi;
    }
    ((n--))
done;

UtahJarhead · Accepted Answer · 2012-04-14T21:28:29.210

3

If you're using bash, you'll want to use [[ and ]] instead of [ and ]. It makes it much easier to do comparisons like you're doing here.

First, what is $n's starting value?

Try this:

ssh usr@host 'for n in {10..1}; do [[ -d /backup/$(($n-1)) ]] && /bin/mv /backup/$(($n-1)) /backup/${n}; done'

That right there should do it. That's assuming your starting number is 10. Depending on where $n is coming from, that can be modified. Notice that mv has the full path specified... this is because when you execute a remote session in ssh, it tends not to execute your .bashrc and .bash_profile meaning you don't have a ${PATH} yet set. There might be a way around it, but I don't know what it is.

Written out more human-readably:

for n in {10..1}
do
  if [[ -d /backup/$src ]]
  then
    /bin/mv /backup/$src /backup/$dst
  fi
fi

Since you're executing it remotely, I figured it would be easier in a single line.

edited Apr 14 '12 at 21:28

answered Apr 14 '12 at 20:06

UtahJarhead

908
7
14

This is in line with what I'm trying but, I get `syntax error near unexpected token `do'` – I Forgot Apr 14 '12 at 21:06
I screwed it up, I apologize. Swap the " with ' – UtahJarhead Apr 14 '12 at 21:28
Look at the current version. I tested it on my side (with commands other than `mv`) and this works perfectly on my side. Notice I removed /bin/bash – UtahJarhead Apr 14 '12 at 21:29

score 2 · Answer 2 · edited Apr 13 '17 at 12:14

2

Place the script in a file on your local machine, e.g. backup.sh and run the remote execution like this:

ssh user@remotehost < backup.sh

This allows you to run the script on the remote host without actually copying it to the remote host.

I use this method for gathering hardware specifications from remote systems.

edited Apr 13 '17 at 12:14

Community

1

answered Apr 14 '12 at 20:14

ewwhite

194,921
91
434
799

Thanks. This could work, but I am trying to keep it all in one script rather than scripts calling scripts. – I Forgot Apr 14 '12 at 21:07
Encapsulating this in a file will be the most maintainable and human-readable/modular approach. – ewwhite Apr 14 '12 at 21:10
You can do `ssh user@host < – arjarj Apr 14 '12 at 21:10
I agree that this should have worked. But, there are all sorts of interpreter and piping issues. Thanks anyway – I Forgot Apr 14 '12 at 21:53

Bash loop to move directories on a remote host via ssh

2 Answers2