thanks for the reply......the code is working fine.....ur code is :

awk ' { if ( NR == 1 ) { head=substr($0,1,300);} else { last = substr($0,1,300);} arr[i++]=$0; }END{ printf "Header is : %-300s Trailer is : %-300s\n", head, last; for( x=1; x<i-1; x++) { print arr[x] } }' old_file > new_file


The problem remains still the same ......for example if there are 1000 rows, one header and one trailer.......it concatenates hearder and trailer in one line and then copies this along with other 1000 rows to new file.......thus cuasing a lot of I/O........i have millions of records in the file and cannot afford to transfer one million records just for the sake of 2 lines (i.e. header and trailer)................

Before this, i got this code:

awk ' { if ( NR == 1 ) { head=$0 } else { last = $0 } }END{ printf "%-300s %-300s\n", head, last }' old_file > new_file
sed '1d;$d' old_file >> new_file

the above code has the same problem that it appends all the data rows................pls note that output is coming fine in both cases but I am concerned about the performance................all we need to do is:

1-Get header in old file (say string1)
2-Get trailer in old fine (say string2)
3-concatenate string1 and string2 (say the result is string3)
4-update the header in old file with string3
5-delete the trailer in old file.

Thanks....