Correct code-like snippet in documentation

[perl5.git] / ext / NDBM_File / 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