awk print Consecutive Number Range : Start and End Range

Question

Please help to print consecutive number ranges like [Start –End] ..,

Sample Input

10
11
12
13
14
17
30
31

Desired output

10-14
17-17
30-31

Thanks in advance

Answer 1

$ awk 'NR==1 {a=$1;b=$1;next} ($1 != b+1){print a,"-",b; a=$1} {b=$1} END{print a,"-",b}' numbers
10 - 14
17 - 17
30 - 31

The above has two variables a and b. a is the first number in the range. b is the last number in the range that has been seen so far.

In awk, NR is the line (record) number. The first part of the awk program just initializes the a and b variables with from the first line: NR==1 {a=$1;b=$1;next}

The next section of the program, ($1 != b+1){print a,"-",b; a=$1}, checks to see if a new range has started. If so the old range is printed and a is updated.

Regardless of whether a new range has started or not, b is updated to the value in the current line: {b=$1}.

After the last line has been seen, the END block is executed. It just prints out the last range.