sed_shell_vars

Here Strings
Similar to heredoc, use 
 COMMAND <<< STRING
syntax to use a string literal as input via stdin for the proceeding commaand.
Similar to using 

 $ echo "Here is a sentence" | sed 's/a/one/'

Here is a method for outputting an altered variable.
Notably it is shell agnostic.

 $ var="Here is a sentence."
 $ sed 's/a/one/' <<< $var
 Here is one sentence.