#!/bin/bash -x
ssh -T root@jumpbox ssh -T root@IP << EOF
YY=$(date +'%y')
echo $YY
EOF
OUTPUT:
Trying tunnel from jumpbox...
Pseudo-terminal will not be allocated because stdin is not a terminal.
-bash: line 6: YY: command not found
The variable I need to assign is more complex, it's not about year number as shown in my description.
When you don't quote the EOF in <<EOF, expansions are perfomed by the local shell inside the here document (so the $(date ...) is expanded by the local date and $YY is expanded to the value in the local shell (empty unless you have assigned a value earlier)). If you the content of the here-document to be passed verbatim to the remote shell, you need to quote the EOF one way or another:
ssh -T root@IP << 'EOF'
YY=$(date +'%y')
echo "$YY"
EOF
