print only lines with unique fields, keep track of count

uniq_fields_with_count.awk

#one-liner awk 'NR == 1 {lastfield = $1; matchline = $0; count = 1; next} {if (lastfield != $1) {print count " " matchline; count = 0; matchline=$0; } count += 1; lastfield = $1} END {print count " " matchline}' inp.txt

NR == 1 {
  lastfield = $1; 
  matchline = $0; 
  count = 1; 
  next
} 

{
  if (lastfield != $1) {
    print count " " matchline; 
    count = 0; 
    matchline=$0; 
  } 

  count += 1; 
  lastfield = $1
} 

END {
  print count " " matchline
}