subshell ``, $() check differences

subshelltest.sh

#!/bin/bash

a=abc!!
echo a=[$a]
echo ""

result=`echo $a | sed -e 's/!/\\\\!/g'`
echo \`~\`=[$result]
echo ""

result=$(echo $a | sed -e 's/!/\\\\!/g')
echo \$\(~\)=[$result]
echo ""


# > a=[abc!!]
# > 
# > `~`=[abc\!\!]
# > 
# > $(~)=[abc\\!\\!]