mjhjmtu

I am trying to execute a script on a remote host through SSH. The script uses environment variables that are set on the local shell. The variables in the script are not expanded.

ssh user@host 'bash -s' < script.sh

Contents of script.sh:

#!/bin/bash

docker pull "$IMAGE"

On the remote host this is executed as:

docker pull ""

As indicated by the error output:

Error parsing reference: "" is not a valid repository/tag: repository name must have at least one component

I've tried to use command substitution:

ssh user@host < $(cat script.sh)

Which leads to:

bash: line 95: $(cat script.sh): ambiguous redirect

How can I make the variables in script.sh expand before passing the commands over SSH?

You can in principle send environment variables to the remote over SSH, but at least OpenSSH disallows it on the server, and doesn't try to send any from the client. The relevant configuration options are AcceptEnv in sshd_config (server) and SendEnv in ssh_config (client).

Assuming you can't or don't want to change the configuration there, since you're sending a whole script to the stdin on the remote anyway, you could also stick the variable assignments in front of that script.

We can use export -p to print out all the exported variables in the current shell, in a format that the remote shell can use to assign them there. Then the remote can process the script as usual, with the variables set.

So with script.sh containing

echo "$FOO" "$HOSTNAME"

This would export FOO in the local shell, and then pass the definitions of all exported variables to remote, along with the script itself. The resulting output contains the value of FOO that was just set.

$ export FOO=abc123
$ (export -p; cat script.sh) | ssh user@remotehost 'bash -s' 
FOO: abc123 HOSTNAME: remotehost

_{(There's a slight problem with Bash here. In normal mode, its export -p prints out declare commands instead of the standard export, and those may not be supported by other shells. So if your local shell is Bash, and you'd start a standard sh on the remote, you'd get errors.)}