Question

The script pasted below causes the following error:

cat: can’t open ‘/tmp/drive/P0.RAW’: No such file or directory

It looks like the script does not properly evaluate $N for the filename.
How $N be made to evaluate so the file name is something like P01L.RAW, P02L.RAW, etc.?

N=1
until [ $N -ge 10 ]; do
    cat bmpheader.bmp /tmp/drive/P0$NL.RAW > ./P0$NL.bmp
    ./quality_metric_test ./P0$NL.bmp
    N=$((N + 1))
done

Answer 1

Your problem is that bash interprets all uppercase characters as part of the variable by default, so it’s looking for $NL instead of just $N. This is why it returns just P0.RAW, as $NL is an unexisting variable. You can easily avoid that by a minor syntax adjustment, call the variable with curly brackets ({ and }) around it. Replace this:

cat bmpheader.bmp /tmp/drive/P0$NL.RAW > ./P0$NL.bmp
./quality_metric_test ./P0$NL.bmp

With this:

cat bmpheader.bmp /tmp/drive/P0${N}L.RAW > ./P0${N}L.bmp
./quality_metric_test ./P0${N}L.bmp

That should do the trick.