>>166
なんかプラスが入った時おかしいっすね

GNU sed
$ pattern='+'
$ echo "$pattern" | sed "s/$(echo "${pattern}" | sed -r 's/([-*+^.$/\]|\[|\])/\\\1/g')/foo[2]/g"
foo[2]

$ pattern='a+'
$ echo "$pattern" | sed "s/$(echo "${pattern}" | sed -r 's/([-*+^.$/\]|\[|\])/\\\1/g')/foo[2]/g"
foo[2]+

busybox sed
# pattern='+'
# echo "$pattern" | sed "s/$(echo "${pattern}" | sed -r 's/([-*+^.$/\]|\[|\])/\\\1/g')/foo[2]/g"
sed: bad regex '\+': Repetition not preceded by valid expression