How to rename multiple files by adding word from that file?

I have files :

file name: report_2020-10-13-17-11.txt
Contain :
…
this report was prepared by=John
…
file name: report_2020-10-13-17-12.txt
Contain :
…
this report was prepared by=Doe
…
file name: report_2020-10-13-17-13.txt
Contain :
…
this report was prepared by=Ton
…
file name: report_2020-10-14-07-25.txt
Contain :
…
this report was prepared by=Bolt
…

I want to rename the files become

John_report_2020-10-13-17-11.txt
Doe_report_2020-10-13-17-12.txt
Ton_report_2020-10-13-17-13.txt
Bolt_report_2020-10-14-07-25.txt

thanks

---

Answer

for file in report_*.txt; do
    owner=$( grep -Po '(?<=this report was prepared by=)\w+' "$file" )
    echo mv "$file" "${owner}_$file"
done

Attribution
Source : Link , Question Author : Mayang Sari , Answer Author : glenn jackman