Editing part of the string

Shell Programming and Scripting
1

Hi guys got a problem here hope u all can help me. I learn that sed can actually edit a string but you need to know the old attribute to change to new 1.
Example:

 sed "s/$title:$author/$title:$Nauthor/g" 

"Harry Potter - The Half Blood Prince:J.K Rowling:40.30:10:50"

Each delimiter : represent 1 new attribute.
can i change 40.30 without knowing it 40.30 but using it position to change??

2

From BookDB.txt? ))) This is at least the third question for the last two days.

Yes, you can. If you will study good. :rolleyes:

3

Is it? =.= but my shell coding one/two day lesson only then assignment came!! i try my very best to learn from google.com but really cannot solve this part =( help pls !!

4

From the command line:

$ awk -v var="YOUR PRICE" '
BEGIN { FS=OFS=":" }  
/^Harry Potter/ { $3=var }
{ print }
'  BookDB.txt

But please don't ask me how this works.
Or with sed:

$ var="YOUR PRICE"; sed -n '/^Harry Potter/s/[^:]*:/'"$var"':/3p' BookDB.txt
5

Thank!! i will go google and learn what each symbol mean