#!/bin/bash
s='[the name of the link](www.example.com/a badly named thing)'
sed -e ':a' -e 's/\(\[[^][]*]([^()[:space:]]*\)[[:space:]]\{1,\}\([^()]*)\)/\1-\2/' -e 'ta' <<< "$s"
IyEvYmluL2Jhc2gKcz0nW3RoZSBuYW1lIG9mIHRoZSBsaW5rXSh3d3cuZXhhbXBsZS5jb20vYSBiYWRseSBuYW1lZCB0aGluZyknCnNlZCAtZSAnOmEnIC1lICdzL1woXFtbXl1bXSpdKFteKClbOnNwYWNlOl1dKlwpW1s6c3BhY2U6XV1cezEsXH1cKFteKCldKilcKS9cMS1cMi8nIC1lICd0YScgPDw8ICIkcyI=