Shell Programming and Scripting

Is there any way that we can fix first 300 characters for header and then 300 characters for trailer no matter how long or short is the actual data.......i.e. if header/trailer length is less than 300 characters, it should append white spaces and if it is more than 300 characters, it should ignore the chacaters>299....................and all the things in the first line........

Then you can modify the awk command as

Code:

awk '{ if ( NR == 1 ) { head=substr($0,1,300);} else { last = substr($0,1,300);}END{printf "Header is : %-300s Trailer is : %-300s\n", head, last}' filename

Output like

Code:

 Header is : Test                                                                                                      Trailer is : Tail

I am not sure it will restrict the output to 300 chars. Check that out

thanks a lot......it is working perfect......now only one issue left of performance..............the situation was like this:

Header
Record 1
Record 2
.......
Record n
Tail

The above code awk '{ if ( NR == 1 ) { head=substr($0,1,300);} else { last = substr($0,1,300);}END{printf "Header is : %-300s Trailer is : %-300s\n", head, last}' filename converted Header and Trailer in first line and within 300 character each.

Now I want to overwrite this one line above (Header+ Tail) over the first line of original file (orginal header) and delete the Tail........i can copy this header and tail to new file and then append Record 1 to Record n to this new file, but that will cause too low performance........so I think better to update first and the last line of the this file.................so how can i do that?

i.e. 1-update the header with new header+trailer
2-delete the tail in original file (may be using cut tail -1 filename?)