from the activeperl manual that I have...
You can put a |'+'| in front of the |'>'| or |'<'| to indicate that you
want both read and write access to the file; thus |'+<'| is almost
always preferred for read/write updates--the |< '+|' >> mode would
clobber the file first. You can't usually use either read-write mode for
updating textfiles, since they have variable length records. See the
*-i* switch in the perlrun manpage <cid:[email protected]>
for a better approach. The file is created with permissions of |0666|
modified by the process' |umask| <cid:[email protected]>
value.
If I read that right "+<" should be used.
I changed the code to use "my $file = '+<mailstats.dat';" and ran it
with a seek of 128, then 30, 1, and 60 and got the following.
This is a test record. This is a test record. This is a
test record. This is a test
record.
When I tried with +> the previous write was lost, but the seek worked.
good luck.
Ken Cornetet wrote:
> I think your oddball way of opening the file may be a problem (use strict
> complains about it). Also, you want ">" not ">>" since that says to always
> append your writes to the end of the file.
>
> You may want binmode as well.
>
> This appears to work
>
> use strict;
> use warnings;
>
> my $file = '+>mailstats.dat';
>
> if (open MAILSTATS, $file) {
> if (seek MAILSTATS, 128, 0) {
> print "Current file position is ", tell(MAILSTATS), "\n";
> print MAILSTATS "This is a test record.";
> } else {
> print " Can not seek to location 128.\n";
> }
>
> close MAILSTATS;
> }
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Barry Brevik
> Sent: Friday, July 17, 2009 3:02 PM
> To: [email protected]
> Subject: Help with file stuff
>
> I'm creating a file which is just an ASCII text file, but I'm writing
> fixed length records into it. At any time, I need to reopen the file and
> write a record to a byte position calculated at run time. The write
> position will frequently be beyond the end of the current file length,
> so I need for the file to be extended.
>
> In the test code below, I have replaced the calculated position with
> "128" for convenience. When I run the code, it creates the file, and it
> says that the current position is "128", but when I write the record, it
> always ends up at the very beginning of the file.
>
> Any clue as to what I am doing wrong?
> ------------------------------------------
> use warnings;
> $MAILSTATS = '+>>mailstats.dat';
>
> if (open MAILSTATS)
> {
> if (seek MAILSTATS, 128, 0)
> {
> print "Current file position is ", tell(MAILSTATS), "\n";
> print MAILSTATS "This is a test record.";
> }
> else
> {
> print " Can not seek to location 128.\n";
> }
>
> close MAILSTATS;
> }
>
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