#!/bin/bash
s=''
sed 's;\(!\|^\)\(\[.*](\)/\(uploads/\);\1\2\3;g' <<< "$s"
sed -E 's;(!\[.*])(\(/uploads/);\1(uploads/;g' <<< "aaa aaa \ aaa aaa"
IyEvYmluL2Jhc2gKcz0nIVtzb21ldGhpbmddKC91cGxvYWRzL3NvbWV0aGluZ2Vsc2UpJwpzZWQgJ3M7XCghXHxeXClcKFxbLipdKFwpL1wodXBsb2Fkcy9cKTtcMVwyXDM7ZycgPDw8ICIkcyIKCnNlZCAtRSAnczsoIVxbLipdKShcKC91cGxvYWRzLyk7XDEodXBsb2Fkcy87ZycgPDw8ICJhYWEgYWFhIFwhW2FhYV0oL3VwbG9hZHMvYWFhL2FhYSkgYWFhIGFhYSI=