January 15, 2012

trouble with name increment

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Hi,
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.

filename="~/Bureau/essai"

index=1 #I will deal with the incrementation of index after this part works

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}

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 ?"