a='abc'
r=${a//b/\041#}
echo $r
echo ${a//b/\041#}
echo "${a//b/\041#}"

a='abc'
r=${a//b/\\041#}
echo $r
echo ${a//b/\\041#}
echo "${a//b/\\041#}"

a='abc'
b='\041#'
r=${a//b/$b}
echo $r
echo ${a//b/$b}
echo "${a//b/$b}"

a='abc'
b='\'
r="${a//b/$b}"
echo $r
echo ${a//b/$b}
echo "${a//b/$b}"

a='abc'
b='\\'
r="${a//b/$b}"
echo $r
echo ${a//b/$b}
echo "${a//b/$b}"

a='abc'
b='\t'
r="${a//b/$b}"
echo $r
echo ${a//b/$b}
echo "${a//b/$b}"
echo ${a//b/\t}
echo "${a//b/\t}"