How can I have both local and remote variable in an ssh command? For example in the following sample code:
A=3;
ssh host@name "B=3; echo $A; echo $B;"
I have access to A but B is not accessible.
But in the following example:
A=3;
ssh host@name 'B=3; echo $A; echo $B;'
I don't have A and just B is accessible.
Is there any way that both A and B be accessible?
I think this is what you want:
A=3;
ssh host@name "B=3; echo $A; echo \$B;"
When you use double-quotes:
Your shell does auto expansion on variables prefixed with $, so in your first example, when it sees
ssh host@name "B=3; echo $A; echo $B;"
bash expands it to:
ssh host@name "B=3; echo 3; echo ;"
and then passes host@name "B=3; echo 3; echo ;" as the argument to ssh. This is because you defined A with A=3, but you never defined B, so $B resolves to the empty string locally.
When you use single-quotes:
Everything enclosed by single-quotes are interpreted as string-literals, so when you do:
ssh host@name 'B=3; echo $A; echo $B;'
the instructions B=3; echo $A; echo $B; will be run once you log in to the remote server. You've defined B in the remote shell, but you never told it what A is, so $A will resolve to the empty string.
So when you use \$, as in the solution:
\$ means to interpret the $ character literally, so we send literally echo $B as one of the instructions to execute remotely, instead of having bash expand $B locally first. What we end up telling ssh to do is equivalent to this:
ssh host@name 'B=3; echo 3; echo $B;'
A=3; ssh -v host@name "B=5; echo $A; echo \$B;" 2>&1 | grep -A 2 'Sending command' or sh -xc 'A=3; ssh host@name "B=5; echo $A; echo \$B;"'.
ssh host@name 'B=\$(find . -name "*.txt"); echo \$B'