Bash字符串替换给了我"bad substitution"

Question

我有一个变量，是一个url，我想在bash中替换url的一部分，但我一直得到"坏替换"

URL="http://hostname/project/branches/Old_Branch/package"
SRC="Old_Branch"
REP="New_Branch"
echo ${$URL/$SRC/$REP};
# desired output is http://hostname/project/branches/New_Branch/package

Answer 1

URL="http://hostname/project/branches/Old_Branch/package"
SRC="Old_Branch"
REP="New_Branch"
echo "${URL/$SRC/$REP}"

注意${} =)中URL没有$符号