linux - Unable to use local and remote variables within a heredoc or command over SSH

Question

Below is an example of a ssh script using a heredoc (the actual script is more complex). Is it possible to use both local and remote variables within an SSH heredoc or command?

FILE_NAME is set on the local server to be used on the remote server. REMOTE_PID is set when running on the remote server to be used on local server. FILE_NAME is recognised in script. REMOTE_PID is not set.

If EOF is changed to 'EOF', then REMOTE_PID is set and `FILE_NAME is not. I don't understand why this is?

Is there a way in which both REMOTE_PID and FILE_NAME can be recognised?

Version 2 of bash being used. The default remote login is cshell, local script is to be bash.

FILE_NAME=/example/pdi.dat
ssh user@host bash << EOF
# run script with output...
REMOTE_PID=$(cat $FILE_NAME)
echo $REMOTE_PID
EOF
echo $REMOTE_PID

Answer 1

You need to escape the $ sign if you don't want the variable to be expanded:

$ x=abc
$ bash <<EOF
> x=def
> echo $x   # This expands x before sending it to bash. Bash will see only "echo abc"
> echo $x  # This lets bash perform the expansion. Bash will see "echo $x"
> EOF
abc
def

So in your case:

ssh user@host bash << EOF
# run script with output...
REMOTE_PID=$(cat $FILE_NAME)
echo $REMOTE_PID
EOF

Or alternatively you can just use a herestring with single quotes:

$ x=abc
$ bash <<< '
> x=def
> echo $x  # This will not expand, because we are inside single quotes
> '
def