in reply to Quick Question - Append File at Beginning?

"Appending" to the beginning of a file. Is that a FAQ?

The operation you request is not typically supported by underlying filesystem. OS/400 I think supports record-based filesmembers where you can insert/delete with abandon? For ext4, etc., this operation will be both costly and inherently dangerous.

This said, in case you insist on DWIM, a simple mmap can do the trick, provided it is available.
Update: use map_handle instead of map_file. 

no warnings;
use File::Map ':all';

open(my $fh, '+>>', shift) or die; # open/mmap modes must ~~
my $off = $fh->tell;
print $fh join " ", @ARGV;
$fh->flush;

# rotate in place
map_handle(my $mmap, $fh, '+<');
substr($mmap, 0, 0, substr($mmap, $off));

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Prev version:
no strict;
no warnings;
use File::Map ':all';

my $fnam = shift @ARGV or die;
open(my $fh, '>>', $fnam) or die;
my $off = -s $fh;

print $fh join " ", @ARGV;
close $fh; # !

# rotate in place
map_file my $mmap, $fnam, '+<';
substr($mmap, 0, 0, substr($mmap, $off));

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Re^2: Quick Question - Append File at Beginning?
by hippo (Archbishop) on Nov 16, 2013 at 11:12 UTC
    "Appending" to the beginning of a file. Is that a FAQ?

    Indeed it is.

[reply]

      I believe that the relavent FAQ is much easier to find with the tool perldoc.

      perldoc -q "append to the beginning of a file"
      Bill
[reply]
[d/l]
        Greetings,

        How does *NIX MBOX deal with data? Would the way it does it, offer some interesting methods.

        Just a thought.

        --Chris

        #!/usr/bin/perl -Tw
use Perl::Always or die;
my $perl_version = (5.12.5);
print $perl_version;
[reply]

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