How to use SED without a file with an env var?

Question

Is it possible to substitute a thing in env var with SED?

$ a='aoeua'
$ sed 's@a@o@g' <$a
bash: aoeua: No such file or directory
$ env|grep "SHELL"
SHELL=/bin/bash

The output I want is

ooeuo

replacing each a in 'aoeua' with o.

Answer 1

This might work for you:

a='aoeua'
sed 's@a@o@g' <<<$a
ooeuo

<<<$a is a here-string

Answer 2

Use echo:

$ echo "$a" | sed 's@a@o@g'

In bash you can also do simple substitutions with the ${parameter/pattern/string} syntax. For example:

$ v='aoeua'
$ echo ${v/a/o}
ooeua

Note that this only replaces the first occurrence of the pattern.