Minor Calculation Error

Shell Programming and Scripting
1

Hello everyone!! I got a slight problem doing some calculation from the text file. I able to get the specific data by cutting it using grep and cut.
The amount can be calculated but the problem I faced now is even the field which I didnt cut is been calculated too.
This is what I meant.

The original
Record: Name: Price: QtyAvailable: QtySold:
SampleA A 10 10 2
SampleB B 20 30 10

User input qtySold :2 for sample A(The correct way)

Record: Name: Price: QtyAvailable: QtySold:
SampleA A 10 8 2
SampleB B 20 30 10

Problem facing now.. Notice the price is also minus.

Record: Name: Price: QtyAvailable: QtySold:
SampleA A 8 8 4
SampleB B 20 30 10

Text file(file.txt)
SampleA:A:10:10:2
SampleB:B:20:30:10

echo -n "Record: "
    read rec
    echo -n "Author: "
    read author
    if grep -q "$rec:$author" "file.txt"; then
    echo -n "No. of copies sold: "
    read sold
    qtyA=`grep -w "$rec:$author" file.txt | cut -d: -f4`
    qtyS=`grep -w "$rec:$author" file.txt | cut -d: -f5`
    echo "Current Record info:"
    awk -F: -vOFS=", " -vt="$rec:$author" '$0~t{$3="$"$3;print}' file.txt
    echo "New Record info:"
    cQtyA=`expr $qtyA - $sold`
    cQtyS=`expr $qtyS + $sold`
    sed "s/$qtyA/$cQtyA/g" file.txt > file1.txt && mv file1.txt file.txt
    sed "s/$qtyS/$cQtyS/g" file.txt > file1.txt && mv file1.txt file.txt

    awk -F: -vOFS=", " -vt="$rec:$author" '$0~t{$3="$"$3;print}' file.txt
    else
    echo "Record not found!"
    fi

Seems that I correctly cut the specific field yet I can't calculate properly. Haha sorry for the trouble.

2

Try to use:

cQtyA=$(($qtyA - $sold))
cQtyS=$(($qtyS + $sold))

This is POSIX correct and all modern shells should work with these expressions. But I don't know whether it helps or not.

3

Ahh its still the same.. The price of the record still reduce though.. Is the extraction of the data wrong?