Chris Coggins wrote:
I posted a question to this list yesterday from the google groups
interface, asking for help with the following. I have since tried to
post additional details in replies to that message using the google
groups site and none of my posts have shown up on the list so let's try
this again the right way.
I have a datafile with 1 line of data, 30 numbers delimited by tildes.
(Sample code below only uses 4 numbers to save time)
I need to open this file, grab this line of data, split it into
individual numbers, perform some simple math (addition) on each
number, and then put the new values back into the datafile, replacing
the original data that was there.
I neglected to mention in my original post that I need to access these
new values elsewhere in the script to perform additional math functions
with them.
I've tried several variations of the code below, including using arrays,
and none of them got through without the script failing. The new
datafile gets written, but it merely contains a ~. The errors I get are
"use of uninitialized values in such and such line" and "variables needs
explicit package name". When the script does run, the variables lose
their values as soon as I close the file after inhaling it, making all
the rest of the actions in the subroutine futile.
the datafile used below initially contains 30 values that were written
previously, and this has been verified over and over.
sub newValues {
my($file) = shift;
open(FILE, "<$file") or die("Unable to open data file.");
while (<FILE>) {
my($a,$b,$c,$d) = split(/~/, $_);
$a = $a+$previousarray[4]; # I've tried to perform this math action
after close(FILE) and get the same result -> failure.
$b = $b+$previousarray[7];
$c = $c+$previousarray[0];
}
close(FILE);
open(FILE, ">$file") || die ("unable to open file");
print FILE ("$a~$b~$c \n");
close(FILE);
}
#end sub
Now my datafile just contains a single tilde and no values. I've also
tried to bring the original data from the datafile into my(@array) and
get the same errors.
Keep in mind I need other subroutines to be able use these new values,
but these local variables lose their values once the file is closed.
I've also tried to declare them as global variables but I'm not doing
something right because the script won't execute.
I really need some help figuring this out if somebody would be kind
enough to help a novice.
Hello Chris
Your lexical variables $a, $b, $c are local to the 'while' block, and do
not exist outside it. Error "Global symbol xx requires explicit package
name" is because the variable is not declared. Error "Use of
uninitialized value..." is because Perl uses a value of 'undef' where
variables are missing.
As an aside it is bad form to use meaningless variable names, and $a and
$b are special names that are used by core Perl so should be avoided.
Also it is prefereable to use lexical file handles and the
three-argument form of 'open', and incorporating the standard variable
$! into the die string will give valuable information about why the
operation failed.
Declaring your variables outside the 'while' loop would fix your
problem, but as you are interested only in the first line of the file it
is as well to remove the loop altogether. Take a look at the code below
and see if it meets your requirements.
HTH,
Rob
sub newValues {
my $file = shift;
open my $data, '<', $file or die "Unable to open data file: $!";
my $line = <$data>;
close $data;
my @data = split /~/, $line;
die "Invalid data format" if @data < 3;
$data[0] += $previousarray[4];
$data[1] += $previousarray[7];
$data[2] += $previousarray[0];
open my $out, '>', $file or die "Unable to open output file: $!";
print $out join('~', @data[0,1,2]), "\n";
close $out or die "Failed to close output file: $!";
}
--
To unsubscribe, e-mail: beginners-unsubscr...@perl.org
For additional commands, e-mail: beginners-h...@perl.org
http://learn.perl.org/
