#!/bin/bash
s='/stackoverflow.com/questions/54517334/print-word-after-string'
awk -F'[/.]' '{for(i=1;i<=NF;i++){if($i=="54517334"){print "#"$(i+1)}}}' <<< "$s"
IyEvYmluL2Jhc2gKcz0nL3N0YWNrb3ZlcmZsb3cuY29tL3F1ZXN0aW9ucy81NDUxNzMzNC9wcmludC13b3JkLWFmdGVyLXN0cmluZycKYXdrIC1GJ1svLl0nICd7Zm9yKGk9MTtpPD1ORjtpKyspe2lmKCRpPT0iNTQ1MTczMzQiKXtwcmludCAiIyIkKGkrMSl9fX0nIDw8PCAiJHMi