Convert windows batch to linux

[che10]

Hello guys!
I need help converting two scripts I use on windows to be able to use them on linux, I am new to linux and all of my attempts have failed.

1.

for %%a in (*.mkv) do mkvmerge -o "output\%%~a" --subtitle-tracks ara --default-track 3 "%%~a"

2.

FORFILES /M "*.mkv" /c "cmd /c ffmpeg -ss 5.5 -i  ^"@file^" -c copy -map 0 ^"done\\@file^""

Thanks in advance!