Timothy Johnson wrote:
> Except that it will essentially create a new file. Why did you want
> to avoid writing a new file? As far as I know, you can't just
> "erase" data in the middle of a file. That's just not how they work.
> Someone correct me if I'm wrong. As far as I know, any program that
> does this rewrites the file. The only thing that is somewhat similar
> is that you can do a sysread and change part of a file, but I don't
> think you can remove part of a file without rewriting it.
You are correct. The only way to remove data from the middle of a file is to
rewrite the remainder of the file starting from the point of removal.
You can remove the blank lines 'in-place' without writing to a second file
(which is what Perl's -i does), but you have to do some file pointer
manipulation. Here's an example:
#!/usr/bin/perl
use strict;
use Fcntl qw(:seek);
squeeze(shift @ARGV) while @ARGV;
sub squeeze {
my $fname = shift;
open F, "+<$fname" or die "Couldn't open $fname: $!\n";
my ($p1, $p2);
$p1 = $p2 = tell(F);
while (<F>) {
$p2 = tell(F);
next if /^$/;
seek(F, $p1, SEEK_SET);
print F $_;
$p1 = tell(F);
seek(F, $p2, SEEK_SET);
}
truncate(F, $p1);
close(F);
}
Frankly, the one-liner with perl -i is much preferred.
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