Bash script problem

Hi.
I have a problem with a bash script I need to write for a course. I'm not looking for someone to answer the question for me, I could just do with a little nudge in the right direction.

The task is pretty trivial, but the problem lies with the limited set of tools I have at my disposal. I have to write a bash script that takes two command line arguments, $1 being some text, and $2 being the name of a non-empty file. The script has to insert $1 into the middle of $2 (if it's even then round down).

The only file editing commands allowed are vi and cat; so no sed,ed,awk or anything that would be used in the real world. Also no control structures (if,for....). the only way I can think of doing it is by using vi from the script, but I can't find any clear guide on how to edit with vi from a script. Here is what I've got so far and a sort of rough algo of what I think needs to be done. Please excuse any syntax errors, I'm very new to this but I hope it's clear enough to see what I'm I'm attempting.



I'd really appreciate it if someone who's not a noob like myself could tell me if I'm on the right track and perhaps point me to a reference or tutorial about doing simple editing with vi from a bash script.

Thanks very much.

You cannot use conditional statements? That makes it pretty damn difficult to determine it's a non-empty file etc. I presume from the specifics of this it's a homework assignment of some sort. Due to this I won't give you the solution, rather point you in some helpful directions.
*nix comes with a nice little operator (>) that will allow you to redirect output. This operator is destructive meaning it will overwrite any existing data that may exist where you are re-directing your output to. *nix also has a non-destructive redirection operator that will append instead of replace (>>). This is the important part to placing your input in to a text file.
In regards to Vi, the important thing to remember is it's a text editor. And that is what it does, allows the user to edit text. It does not provide commands or parameters to pass data that can be input in to a file. Unfortunately this is not its intended purpose, so it is useless for this. Looking at your problem Vi is about as useful as a chocolate teapot to it. I suggest you concentrate your efforts on using the above operators.

HTH

Thanks for your reply. In the end I just used 'head -n' and 'tail -n' together with 'cat'. I had to use an 'if' statement to account for files with and odd number of lines, but I couldn't see another way around it.

You cannot achieve this without atleast one IF statement. I'd suggest more than one to check the file is not empty and/or that it exists.

dupe.

I wrote a quick script to prove that you can find the middle of file without using an if:
# $1 is the number of lines in your file:
number=$(( (($1 * 10) / 2) ))
answer=${number:0:$(( ${#number} - 1 ))}

echo "number is: $answer"
EOF

simple and effective.
BTW: to help you with the rest of your issue: cat -n will print line numbers.

Not the entire scenario:

You need some form of conditional statement to check if it's a non-empty (already exists) file.