trouble with name increment



I am trying to write a script that records a window on my screen. No pb with that.
To go further I would like to choose an incremental fileName for output incrementing if the fileName already exist.
I have trouble doing it so before dealing with the incrementation itself, I want to check I can substitute the calculated name in the ffmpeg command.


index=1 #I[B] will deal with the incrementation of index after this part works [/B]

mystring="${fileName}${index}.mkv" #omce I have a proper index I concatenate the name with index and name extension 

echo ${mystring} # gives ~/Bureau/essai1.mkv seems to be what I expect 

ffmpeg -f alsa .....  -y ${mystring}  # gives error message ~/Bureau/essai1.mkv: No such file or directory despite -y to force overwriting

I get this message

~/Bureau/essai1.mkv No such file or directory despite -y to force overwriting
However if I put the file name directly in the command like this


ffmpeg -f alsa .....  -y ~/Bureau/essai1.mkv

it works perfectly. My question is : "What is wrong ?"

Do you have a subdirectory in your home directory named Bureau?

If not, then that's the problem. Execute mkdir Bureau and then run the script again.
Thanks for your answer.

Bureau is the French translation for Desktop and I*can CD to it from terminal. Moreover if the string
 ffmpeg  -f alsa .....  -y ~/Bureau/essai1.mkv
is written directly in the scipt it works fine.

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