I want to be able to us an if statement to evaluate a string using a regular expression. What syntax would I use?

if $["$$string" $=+$ someregex$]$; then

echo "some result"

fi

if $[["$$string" $=$~ someregex$]]$; then

echo "some result"

fi

if $[$

$\{"$$string" $=$$ someregex$\}$; then

echo "some result"

fi

none of the above