Shell Programming and Scripting

abc abcd
abc abcd <some tag> xyx
abcd xyz
abc abcd <some tag> xyx
xyz abc

replaced tag1
replaced tag2

exec 3<file2
   exec 4<file1

   while IFS= read -r line1 <&3
   IFS= read -r line2 <&4
   do

        value_to_be_replaced=`echo "$line1"`
        test=`echo "$line2"`
   if [ "$test" == "abc abcd <some tag> xyx" ]
   then
        sed 's/$test/abc abcd "$value_to_be_replaced" xyx/' $test
  fi
  done

awk '/<some tag>/{getline t < "file2";sub("<some tag>",t,$0)}1' file1