John W.Krahn <[EMAIL PROTECTED]> writes:
> use Fcntl ':seek';
>
> seek FILE, -100, SEEK_END or die "Cannot seek on './myfile' $!";
Still seeing something I don't understand. Using a working version of
the code I posted (included at the end) telling seek to go to 100
bytes before the byte count at eof. I see a small discrepancy in
where it actually goes of 5-15 bytes.
I didn't use Fcntl ':seek' because it appears to lack the other two
operators (SEEK_SET, SEEK_CUR) referred to at perldoc -f seek.
And it seems like what I really needed was SEEK_SET or (zero 0) as
shown at perldoc -f seek. Since using SEEK_END or (2) will give an
unpredictable seeking location because the amount of data entered will
vary every time (a real working version) of this script gets used.
So subtracting the original end of file byte cnt + 100 may not go
where we want to be. Seems like it would be better to tell seek to go
to 100 bytes before the original end of file byte count. So I had that
wrong originally too.
That is what I'm attempting here but as mentioned above it appears to
show an additional offset of 12 bytes from somewhere: OS?
Im running Gentoo linux,
cat ./testseek.pl
===== * ===== * ===== * ===== * =====
#!/usr/local/bin/perl
use strict;
use warnings;
# use Fcntl ':seek';
my $bytes;
open(FILE,"+>>./myfile")or die " Can't open ./myfile: $!";
## Grab the total byte count in this file
$bytes = tell(FILE);
print "Pre seek bytes <$bytes> \n\n";
sleep 2;
print 'We print line\nline\nline\nline\nto ./myfile' . "\n";
print FILE "line\nline\nline\nline\n";
print "Now we subtract 100 from <$bytes>:Getting:" . ($bytes - 100) . "\n";
print 'Setting seek(FILE, ' . ($bytes - 100) . ', 0)' . "\n\n";
## go back to 100 bytes before pervious end of file (in bytes).
## Didn't use Fcntl ':see'; because it appears to lack the SEEL_SET or
## SEEK_CUR refered to at perldoc -f seek
seek(FILE, ($bytes - 100) ,0);
sleep 4;
while(<FILE>){
print tell(FILE) . ': Showing bytes per line using tell()' , "\n";
}
close(FILE);
===== * ===== * ===== * ===== * =====
> wc -c myfile
137 myfile
> ./testseek.pl
Pre seek bytes <137>
We print line\nline\nline\nline\nto ./myfile
Now we subtract 100 from <137>:Getting:37
Setting seek(FILE, 37, 0)
49: Showing bytes per line using tell()
50: Showing bytes per line using tell()
51: Showing bytes per line using tell()
62: Showing bytes per line using tell()
86: Showing bytes per line using tell()
88: Showing bytes per line using tell()
110: Showing bytes per line using tell()
111: Showing bytes per line using tell()
123: Showing bytes per line using tell()
137: Showing bytes per line using tell()
142: Showing bytes per line using tell()
147: Showing bytes per line using tell()
152: Showing bytes per line using tell()
157: Showing bytes per line using tell()
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