LinuxQuestions.org - Parameter substitution in loops

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Parameter substitution in loops

I'm trying the following loop to process a bunch of files and create a new filename for the output file, but it's not working. Also, I want to make the new value for TT to be five digits, with a leading zero.

Basically, I need to extract every 10 thousandth line from a bunch of input files. In each output file, I want to include a 5 digit line number in each output file's filename (so I know where it came from).

My current code just hangs (on further inspection, it created a whole bunch of strangely named files which I now must get rid of).

Code:

for ((TT=10000; TT<=100000; TT+=10000))

do

        for fn in *U.csv;

        do

                prefix=${fn%tol*}

                suffix="t=$TT_forward.LC.csv"

                nfn=$prefix$suffix

                echo "$nfn"



                echo head -n "$TT" "$fn" | tail -n 1 >"../$nfn"

        done

done

Actually, I have it almost working (so there!, all you experts). I still need a five digit number in the first iteration.

Code:

for ((TT=9999; TT<30000; TT+=10000))

do

        for fn in N=0008_Beta=0[456]*.csv;

        do

                prefix=${fn%tol*}

                suffix="t=${TT}_forward.LC.csv"

                nfn=$prefix$suffix

                echo $prefix

                echo $suffix

                echo $nfn



                echo "head -n '${TT}' '$fn' | tail -n 1 >../'$nfn'"

        done

done

On third thought, nevermind. It seems I need the 10,000th line and every 10 thousand after that. So I don't even have to pad the zeros.

I would probably use awk with NR%10000, then you need neither loop (as awk will handle it) and then just process the files as required.