linux - Check variables from different lines with awk

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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

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.