Shell Programming and Scripting

 CAR 23
COLOR 12
CAR 44
COLOR 12
CAR 55
COLOR 20
SIZE BIG
CAR 56
CAR 57
COLOR 11

CAR 23 COLOR 12
CAR 44 COLOR 12
CAR 55 COLOR 20 SIZE BIG
CAR 56 
CAR 57 COLOR 11

awk '/CAR/ && C { print C ; C=$0 ; next } { C=C" "$0; } END { if(C) print C }' inputfile

 cat inputfile | tr '\n' ' '  | sed 's/ CAR /\nCAR /g; s/ $/\n/'

sed '
  s/^  *//
  t loop
  :loop
  $b
  N
  s/ *\n *CAR /\
CAR /
  t p
  s/ *\n */ /
  t loop
  :p
  P
  s/.*\n//
  t loop
 ' in_file >out_file

awk ' {
        $1 = $1
        A[++n] = $0
} END {
        for ( i = 1; i <= n; i++ ) {
                if ( A[i] ~ /CAR/ ) {
                        A[i] = ( i == 1 ? A[i] FS : RS A[i] FS )
                        printf A[i]
                }
                else
                {
                        A[i] = ( i == n ? A[i] RS : A[i] FS )
                        printf A[i]
                }
        }
}' filename