#!/bin/bash
s='2021-05-27 10:40:50.678117 PID529270:TID 47545543550720:SID 1673488:TXID 786092740:QID 140: INFO:MEMCONTEXT:MemContext state: mem[cur/hi/max] = 9135 / 96586 / 96576 MB, VM[cur/hi/max] = 9161 / 21841178 / 100663296 MB'
sed -En 's~.*= ([0-9]+) /.*=.*~\1~p' <<< "$s"
IyEvYmluL2Jhc2gKcz0nMjAyMS0wNS0yNyAxMDo0MDo1MC42NzgxMTcgUElENTI5MjcwOlRJRCA0NzU0NTU0MzU1MDcyMDpTSUQgMTY3MzQ4ODpUWElEIDc4NjA5Mjc0MDpRSUQgMTQwOiBJTkZPOk1FTUNPTlRFWFQ6TWVtQ29udGV4dCBzdGF0ZTogbWVtW2N1ci9oaS9tYXhdID0gOTEzNSAvIDk2NTg2IC8gOTY1NzYgTUIsIFZNW2N1ci9oaS9tYXhdID0gOTE2MSAvIDIxODQxMTc4IC8gMTAwNjYzMjk2IE1CJwpzZWQgLUVuICdzfi4qPSAoWzAtOV0rKSAvLio9Lip+XDF+cCcgPDw8ICIkcyI=