Question

I want to combine values from multiple lines with different lengths using awk into one line if they match. In the following sample match values for first field,
aggregating values from second field into a list.

Input, sample csv:

222;a;DB;a
222;b;DB;a
555;f;DB;a
4444;a;DB;a
4444;d;DB;a
4444;z;DB;a

Output:

222;a|b
555;f
4444;a|d|z

How can I write an awk expression (maybe some other shell expression) to check if the first field value match with the next/previous line, and then print a list of second fields values aggregated and separated by a pipe?

Answer 1

awk '
  BEGIN {FS=";"}
  { if ($1==prev) {sec=sec "|" $2; }
    else { if (prev) { print prev ";" sec; };
           prev=$1; sec=$2; }}
  END { if (prev) { print prev ";" sec; }}'

This, as you requested, checks the consecutive lines.