Current File : //usr/lib/x86_64-linux-gnu/perl/5.38.2/NDBM_File.pm
package NDBM_File;
use strict;
use warnings;
require Tie::Hash;
require XSLoader;
our @ISA = qw(Tie::Hash);
our $VERSION = "1.16";
XSLoader::load();
1;
__END__
=head1 NAME
NDBM_File - Tied access to ndbm files
=head1 SYNOPSIS
use Fcntl; # For O_RDWR, O_CREAT, etc.
use NDBM_File;
tie(%h, 'NDBM_File', 'filename', O_RDWR|O_CREAT, 0666)
or die "Couldn't tie NDBM file 'filename': $!; aborting";
# Now read and change the hash
$h{newkey} = newvalue;
print $h{oldkey};
...
untie %h;
=head1 DESCRIPTION
C<NDBM_File> establishes a connection between a Perl hash variable and
a file in NDBM_File format;. You can manipulate the data in the file
just as if it were in a Perl hash, but when your program exits, the
data will remain in the file, to be used the next time your program
runs.
Use C<NDBM_File> with the Perl built-in C<tie> function to establish
the connection between the variable and the file. The arguments to
C<tie> should be:
=over 4
=item 1.
The hash variable you want to tie.
=item 2.
The string C<"NDBM_File">. (Ths tells Perl to use the C<NDBM_File>
package to perform the functions of the hash.)
=item 3.
The name of the file you want to tie to the hash.
=item 4.
Flags. Use one of:
=over 2
=item C<O_RDONLY>
Read-only access to the data in the file.
=item C<O_WRONLY>
Write-only access to the data in the file.
=item C<O_RDWR>
Both read and write access.
=back
If you want to create the file if it does not exist, add C<O_CREAT> to
any of these, as in the example. If you omit C<O_CREAT> and the file
does not already exist, the C<tie> call will fail.
=item 5.
The default permissions to use if a new file is created. The actual
permissions will be modified by the user's umask, so you should
probably use 0666 here. (See L<perlfunc/umask>.)
=back
=head1 DIAGNOSTICS
On failure, the C<tie> call returns an undefined value and probably
sets C<$!> to contain the reason the file could not be tied.
=head2 C<ndbm store returned -1, errno 22, key "..." at ...>
This warning is emitted when you try to store a key or a value that
is too long. It means that the change was not recorded in the
database. See BUGS AND WARNINGS below.
=head1 SECURITY AND PORTABILITY
B<Do not accept NDBM files from untrusted sources.>
On modern Linux systems these are typically GDBM files, which are not
portable across platforms.
The GDBM documentation doesn't imply that files from untrusted sources
can be safely used with C<libgdbm>.
Systems that don't use GDBM compatibilty for ndbm support will be
using a platform specific library, possibly inherited from BSD
systems, where it may or may not be safe to use an untrusted file.
A maliciously crafted file might cause perl to crash or even expose a
security vulnerability.
=head1 BUGS AND WARNINGS
There are a number of limits on the size of the data that you can
store in the NDBM file. The most important is that the length of a
key, plus the length of its associated value, may not exceed 1008
bytes.
See L<perlfunc/tie>, L<perldbmfilter>, L<Fcntl>
=cut
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