Template system in bash

#!/bin/bash
#SED_COMMAND=""
cat stamp | (while read -r l; do
        echo "Line: $l";
        KEY=${l% *}
        VALUE=${l:${#KEY}+1}
        echo "Key: $KEY"
        echo "Value: $VALUE"
        SED_COMMAND=$SED_COMMAND$SEP"s/{{$KEY}}/$VALUE/g"
        echo "SED_COMMAND:$SED_COMMAND"
        SEP=";"
done
sed $SED_COMMAND test.yaml
)