On Sat, Mar 21, 2009 at 11:05, Randal L. Schwartz <mer...@stonehenge.com> wrote:
>>>>>> "Gunnar" == Gunnar Hjalmarsson <nore...@gunnar.cc> writes:
>
> Gunnar> Martin Spinassi wrote:
>>> Is there any way to open a file for input and output at the same time?
>
> Gunnar> Yes. Open it with the '+<' MODE.
>
> Gunnar> open my $fh, '+<', $file or die "Couldn't open $file: $!";
> Gunnar> my @keep;
> Gunnar> while ( <$fh> ) {
> Gunnar> next if /^--/;
> Gunnar> push @keep, $_;
> Gunnar> }
> Gunnar> seek $fh, 0, 0;
> Gunnar> truncate $fh, 0;
>
> And then your power fails at this moment, and you've lost the entire file.
>
> Much safer to use in-place editing. See $^I in perlvar.
snip
Based on my admittedly ignorant reading of the code for Perl 5.8.9, it
looks like in-place editing does not do an fsync after the rename[1].
If this is true, then there is up to a five second window[2] of
opportunity for a similar thing to happen to in-place editing on an
Ext4 filesystem[3].
There is also the ongoing danger of putting untrusted file names in
@ARGV[4], so make sure file names do not contain "|" before putting
them in @ARGV.
1. I have asked about this on p5p in the "So what else is new?" thread.
2. http://tinyurl.com/d9pcfg
3. or any other filesystem that follows POSIX strictly on this point
4. http://perlgeek.de/blog-en/perl-tips/magic-argv.writeback
--
Chas. Owens
wonkden.net
The most important skill a programmer can have is the ability to read.
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