Re: Uninitialized value warning in subrutine

[olivierp]

I assume you would like to access the last element of the implicit @_ array. Note that @_ and $_ are 2 different variables, as @var and $var are.
In a sub, @_ represents the arguments that you passed in, and this is what you should be accessing, whereas $_ is the "default" variable used/created in various looping constructs, the "default" match target , amongst others, as infor (@array){ print $_ if /hello world/i}
Your "Use of uninitialized value in substraction (-)" comes from trying to substract 1 from the $_ variable, which is undefined in the sub, when you actually would like to substract 1 from the number of items in @_
Here are 3 ways of achieving what you are looking for:

# Access directly the last element of the array
sub queryDBI {
    my $query1 = "SELECT $_[2],$_[3],$_[-1] FROM " . $_[1];
    return $query1;
} 
print queryDBI(qw/first second third fourth fifth_and_last/),$/ x 2'

# In scalar context, @array returns the number of elements in contains
+.
# As @array indexes start at 0 (unless someone explicitly changes this
+ through $[), we substract 1
sub queryDBI {
    my $query1 = "SELECT $_[2],$_[3],$_[@_-1] FROM " . $_[1];
    return $query1;
} 
print queryDBI(qw/first second third fourth fifth_and_last/),$/ x 2'

# $#array returns the index of the last element of the array.
sub queryDBI {
    my $query1 = "SELECT $_[2],$_[3],$_[$#_] FROM " . $_[1];
    return $query1;
} 
print queryDBI(qw/first second third fourth fifth_and_last/),$/ x 2'

For further info on predefined variables, as $_ and @_ check out perlvar