increment values in column within file with bash, sed and awk

This could be done more tersely with awk, but pure bash works fine:

last_year=
counter_val=
while IFS=';' read -r year old_counter rest; do
  if [[ $year = "$last_year" ]]; then
    (( ++counter_val ))
  else
    counter_val=1
    last_year=$year
  fi
  printf -v result '%s;' "$year" "$counter_val" "$rest"
  printf '%s\n' "${result%;}"
done <input.txt >output.txt

You simply want to increment your second column, and not add one to it? Do you want the second column to go from one onward no matter what the second column is?

awk -F\; '{
    if ( NR == 1 ) {
        year = $0
    }
    if ( year == $0 ) {
        for (count = 1; count < NF; count++) {
            if ( count == 2) {
                printf NR ";";
            }
            else {
                printf $count ";";
            }
        }
        print "";
    }
    else {
        print 
    }
}' test.txt

Awk is a natural program to use because it operates in assuming a loop. Plus, it's math is more natural than plain shell.

The NR means Number of Records and NF means Number of fields. A field is separated by my -F\; parameter, and the record is the line number in my file. The rest of the program is pretty obvious.

Using awk, set the FS (field separator) and OFS (output field separator) to ';' and for each new year record set the val counter to the start column 2 value. Increment val for each line with that year.

awk -F';' 'BEGIN{OFS=";";y=0} 
 { if (y!=$1) 
      {y=$1;val=$2;print} 
   else 
      {val++;print $1,val,$3,$4,$5,$6,$7}}' data_file