@H_502_9@echo 'first url,second url,third url' | sed 's/.*second//'

编辑：我误解了更好：

@H_502_9@echo 'first url,third url' | sed 's/.*second \([^ ]*\).*/\1/'

要么：

@H_502_9@echo 'first url,third url' | perl -nle 'm/second ([^ ]*)/; print $1'