How to read the comma separated values - unix

Question

We have a fixed width file
Col1 length 10
Col2 length 10
Col3 length 30
Col4 length 40
Sample record
ABC 123 xyz. 5171-5261,51617
ABC. 1234. Xxy. 81651-61761
Col4 can have any number of comma separated values
1 or more within length of 40 characters: If it is has 1 value for that record there is no change in output file.
If more than one value is there i.e. comma separated (5171-5261,51617)
the output file should have multiple records.
1 record
ABC. 123. Xyz. 5171-5261
ABC 123. Xyz. 51617
What is the most efficient way to do this.
As of now trying using while and for loop but it is taking so long for execution since we are doing this splitting by reading each record.
The output file can be comma separated or fixed width.

Answer 1

awk is your friend here.
A single line of awk will achieve what you need:
awk -v FIELDWIDTHS="10 10 30 40" '{ if (match($4,",")) { split($4,array,","); for (i in array) { print $1,$2,$3,array[i]; }; } else { print $1,$2,$3,$4 }; }' samp.dat
For ease of reading the code is:
{
if (match($4,",")) {
split($4,array,",");
for (i in array) {
print $1,$2,$3,array[i];
};
} else {
print $1,$2,$3,$4
};
}
Testing with the sample data you supplied gives:
ABC 123 xyz. 5171-5261
ABC 123 xyz. 51617
ABC. 1234. Xxy. 81651-61761
How it works:
awk reads your file one line at a time.
The FIELDWIDTHS directive allows us to reference each column as $1,$2...
Now that we have our columns we can look for a comma in the fourth field with match($4,",").
If we find one we make an array of the values in the fourth field that are separated by commas with split($4,array,",").
Then we loop through this array and print multiple lines of output, one for each element of the array.
If the fourth field has no comma the else clause prints a single line.
This process repeats for each line in your fixed width file.
NOTE:
awk associative arrays do not guarantee to preserve the order of your data.
This means that your output might come out as
ABC 123 xyz. 51617
ABC 123 xyz. 5171-5261
ABC. 1234. Xxy. 81651-61761
i.e. 5171-5261,51617 in the input data produced a line from the second value before the first.
If the ordering is important to you then you can use the code below that makes a csv from your input data first, then produces the output preserving the order.
awk -v FIELDWIDTHS="10 10 30 40" '{print $1,$2,$3,$4}' OFS=',' samp.data > samp.csv
awk -F',' '{ for (i=4; i<=NF; i++) { print $1,$2,$3,$i } }' samp.csv