Pattern matching

To search from pattern matching 4usXzpWPR1G1Q8PvSmFImg== to OJOH7fOvRiimCgrwgAFoQA== from log.gz files

Actually everything inside slashes are regex pattern.

gzip -cd scheduler.2025-09-12.*.log.gz | sed -n '/4usXzpWPR1G1Q8PvSmFImg==/,/OJOH7fOvRiimCgrwgAFoQA==/p' > log

More powerful with awk.
awk evaluates set of commands.
index($0, "aeq9M/vWSVSt5cMG2DJCKg==") returns position of aeq9M/vWSVSt5cMG2DJCKg== inside $0 which represents the current line.
If the above is true then it sets variable in_block to 1.
awk will start printing any line if the condition is true. And here the condition is in_block which was set as true when we found the first match.

gzip -cd scheduler.2025-09-12.*.log.gz \
  | awk '
    index($0,"aeq9M/vWSVSt5cMG2DJCKg=="){in_block=1}
    in_block
    index($0,"OJOH7fOvRiimCgrwgAFoQA=="){in_block=0}
  ' > log