#!/bin/bash
s='samplename1/filename1 anotherthing/anotherfile asdfgh/hjklñ
2 3 4
5 6 7'
sed '1 s,/[^[:space:]]*,,g' <<< "$s"
IyEvYmluL2Jhc2gKcz0nc2FtcGxlbmFtZTEvZmlsZW5hbWUxICAgYW5vdGhlcnRoaW5nL2Fub3RoZXJmaWxlICAgIGFzZGZnaC9oamtsw7EKICAgICAgICAyICAgICAgICAgICAgICAgICAgICAgICAgMyAgICAgICAgICAgICAgICAgICAgICA0CiAgICAgICAgNSAgICAgICAgICAgICAgICAgICAgICAgIDYgICAgICAgICAgICAgICAgICAgICAgNycKc2VkICAnMSBzLC9bXls6c3BhY2U6XV0qLCxnJyAgPDw8ICIkcyI=