I see two fundamental problems with your script:

1. User input has to be validated
You write the user has to enter the name of the part. That raises the question: what happens, if the part s/he enters is not in the database? It is ok, IMHO, if you say that this is beyond the scope of the homework or that false input can be silently ignored or whatever - it is just a fundamental truth that any input users provide should be validated somehow and you dhould have an answer to this question. If it is the correct data type (strings, digits, ...), if it is "well-formed" in some regard (for instance an IP address looks always the same - 4 numbers, 0-255, divided by 3 dots, etc.), and so on. If your program makes some assumption about which data it will be presented then check if indeed this data is what you have before you use it.

2. The sed-script
There are three basic forms of sed commands:

Code:

s/<expr1>/<expr2>/

/<expr>/ {
       command1
       command2
       ....
     }


/<expr1>/,/<expr2>/ {
       command1
       command2
       ....
     }

The first one is the most simple one: it applies the single command to replace <expr1> with <expr2> to every line. It might be that <expr1> is not part the line and the command will do nothing in this case, but still it is applied to the line (this is necessary to understand how sed works).

The second one is a more complex form: it will successively apply command1, then command2, etc. to lines which contain <expr1>. Of course the "list of commands" could also consist of only one command, in which case you can omit the curly braces and write:

Code:

/expr/command

An example: The following script will change only the lines that start with "abc". The change will be to first replace the "c" in "abc" to "<command1>", the second change will be to replace the line end with "<command2>", which effectively appends this to the end of the line.

Code:

sed '/^abc/ {
          s/c/<command1>/
          s/$/<command2>/
     }' in > out

file in:
========
abc will be changed
abd will not be changed
xxx next line will be changed, but this will not
abc

file out:
========
ab<command1> will be changed<command2>
abd will not be changed
xxx next line will be changed, but this will not
ab<command1><command2>

The third and last form ist the most complex one: it will apply a (list of) command(s) to a range of lines. It will start applying the list of commands when a line containing <expr1> is encountered and will do so on any subsequent lines untl <expr2> is found in a line. Then the commands are not applied to any line until <expr1> is found again, etc.. Similar to the second variant you can replace the list of commands by a single command where you can omit the curly braces:

Code:

/expr1/expr2/ommand

See if you can solve your problem now.

I hope this helps.

bakunin