Shell Programming and Scripting

#!/bin/ksh
savestr=""
# remove first \t, we don't need it
sed "s/^\\\t//" filename | while read line
do
       case "$line" in
               \t*) # \t\t line, so print buffer and empty buffer
                       echo "$savestr"
                       savestr=""
                       ;;
               *)     # not \t\t line, so add current line to the buffer
                       savestr="$savestr$line "
                   ;;
       esac
done
# last line
# if file not end \t\t line, then we have some data in buffer, print it
[ "$savestr" != "" ] && echo "$savestr"

awk '/\\t\\t/{printf("\n");next}{gsub(/\\t/,"");print}END{printf("\n")}' ORS=" " filename

#  sed -e :a -e '$!N;s/\\\t\\\t//;s/\n\\\t/ /;s/\\\t/ /;ta' -e 'P;D' infile
 a tab XXXXXXXXXX e tab YYYYYYYYYYY
 c tab DDDDXXXXXX z tab FFFFFFYYYYYYY

sed -n 'H; $ {g; s/\n//g; s/\\t\\t/\n/g; s/\\t//g; p; }' input_file