Shell Programming and Scripting

#so far my add function works as intended
add()
{
    ...blah blah;
}

# delete is kinda working havn't got all bugs out yet but have tested
# and played around with grep on test files, I have been able to delete
# a line from a file, but what i need it to do is
# search database for match product/brand if no such product exist then
# display error: product: not deleted does not exist
# else remove the record. So can delete it fine, but what I'm not sure of 
# is how to do the test to see if it exist first.
delete()
{
    grep -v "${1}:${2}" $dbfile > ../tmp/tmp
    sort ../tmp/tmp > $dbfile
}

#so what i need to do is test to see if the above command happened?
# i dunno :S

#i have to do the same thing with search functions, find product and find
# brand, both need to print error if they don't exist or, in case of find 
# brand it needs to print each line that matches. which I don't think will be 
# too difficult, just unsure of how to test.

if [ -z (grep "${1}${2}" $dbfile) ]
then
    echo "Error:not deleted:product does not exist in database"
    exit 1
else
    grep -v "${1}${2}" $dbfile > ../tmp/tmp
    cat ../tmp/tmp > $dbfile
fi

MILK - PLAIN:PAULS:4
BREAD - WHITE:TIPTOP:2
BREAD - WHOLEMEAL:TIPTOP:2
MILO - DRINK:NESTLE:3

echo "input search query"
read srch
grep "$srch" xxx > tmp
if [ ! -s tmp ]
then
    echo "unable to find $srch"
else
    grep -v "${srch}" xxx > zxzx
    cat zxzx > xxx
    echo "${srch}:deleted"
fi

if grep -q "${1}${2}" $dbfile
then
    echo "Error:not deleted:product does not exist in database"
    exit 1
else
  ...

if grep "${1}${2}" $dbfile >/dev/null
then
    echo "Error:not deleted:product does not exist in database"
    exit 1
else
  ...

if grep -q "${1}${2}" $dbfile
then
    #delete the line
else
    echo "cannot delete:"
fi