How to reference captures in bash regex replacement -

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how can include regex match in replacement expression in bash?

non-working example:

#!/bin/bash name=joshua echo ${name//[oa]/x\1}

i expect output jxoshuxa \1 being replaced matched character.

this doesn't work though , outputs jx1shux1 instead.

bash> name=joshua   bash> echo $name | sed 's/\([oa]\)/x\1/g'   jxoshuxa

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