UNIX for Dummies Questions & Answers

hi all! new to the forum and i love how nice alot of you are. and i was hoping to get some help. a friend of mine asked me to make him a script for backtrack which is based on slax. it makes a new changes.lzm for the usb system and merges 2 files to update it. now i got that handled but i cant seem to over come the simplest of tasks. you see, my entire scrpit relys of weather or not a file exists and weather its there or not it seems to say it exists... my script is simple for this part

Code:

#!/bin/sh
#this is a script i made to merge two .lzm
#files to keep up to date and to make backtrack easy to use

if [ ! -f /mnt/sdb1/BT3/modules ]; then
    echo "changes.lzm found! mergeing new with old .lzm now..."
else
    echo "changes.lzm not found. building new one now..."
fi

please help im starting to feel like a newbie

A file can exist, but it can be not readable by the current user, or zero-length, or still being written to. All of which cause problems.

[ -r filename ] tells if the user can read the file AND if it exists
[ -w filename ] user can write the file AND it exists
[ -s filename ] file is bigger than zero length and exists.

The still being written to problem is harder. See if the above doesn't get you where you need to be.

wow i feel stupid. i was trying to see if the file DID exist and according to my code...
i the program was trying to see if it did NOT exist. oops lol thanks for the help jim i didnt know about the -s