GDBM_File(3perl) Perl Programmers Reference Guide GDBM_File(3perl)
NAME
GDBM_File - Perl5 access to the gdbm library.
SYNOPSIS
use GDBM_File;
[$db =] tie %hash, 'GDBM_File', $filename, &GDBM_WRCREAT, 0640;
# Use the %hash array.
$e = $db->errno;
$e = $db->syserrno;
$str = $db->strerror;
$bool = $db->needs_recovery;
$db->clear_error;
$db->reorganize;
$db->sync;
$n = $db->count;
$n = $db->flags;
$str = $db->dbname;
$db->cache_size;
$db->cache_size($newsize);
$n = $db->block_size;
$bool = $db->sync_mode;
$db->sync_mode($bool);
$bool = $db->centfree;
$db->centfree($bool);
$bool = $db->coalesce;
$db->coalesce($bool);
$bool = $db->mmap;
$size = $db->mmapsize;
$db->mmapsize($newsize);
$db->recover(%args);
untie %hash ;
DESCRIPTION
GDBM_File is a module which allows Perl programs to make use of the
facilities provided by the GNU gdbm library. If you intend to use this
module you should really have a copy of the gdbm manualpage at hand.
Most of the libgdbm.a functions are available through the GDBM_File
interface.
Unlike Perl's built-in hashes, it is not safe to "delete" the current
item from a GDBM_File tied hash while iterating over it with "each".
This is a limitation of the gdbm library.
STATIC METHODS
GDBM_version
$str = GDBM_File->GDBM_version;
@ar = GDBM_File->GDBM_version;
Returns the version number of the underlying libgdbm library. In scalar
context, returns the library version formatted as string:
MINOR.MAJOR[.PATCH][ (GUESS)]
where MINOR, MAJOR, and PATCH are version numbers, and GUESS is a guess
level (see below).
In list context, returns a list:
( MINOR, MAJOR, PATCH [, GUESS] )
The GUESS component is present only if libgdbm version is 1.8.3 or
earlier. This is because earlier releases of libgdbm did not include
information about their version and the GDBM_File module has to
implement certain guesswork in order to determine it. GUESS is a
textual description in string context, and a positive number indicating
how rough the guess is in list context. Possible values are:
1 - exact guess
The major and minor version numbers are guaranteed to be correct.
The actual patchlevel is most probably guessed right, but can be
1-2 less than indicated.
2 - approximate
The major and minor number are guaranteed to be correct. The
patchlevel is set to the upper bound.
3 - rough guess
The version is guaranteed to be not newer than MAJOR.MINOR.
METHODS
close
$db->close;
Closes the database. You are not advised to use this method directly.
Please, use untie instead.
errno
$db->errno
Returns the last error status associated with this database.
syserrno
$db->syserrno
Returns the last system error status (C "errno" variable), associated
with this database,
strerror
$db->strerror
Returns textual description of the last error that occurred in this
database.
clear_error
$db->clear_error
Clear error status.
needs_recovery
$db->needs_recovery
Returns true if the database needs recovery.
reorganize
$db->reorganize;
Reorganizes the database.
sync
$db->sync;
Synchronizes recent changes to the database with its disk copy.
count
$n = $db->count;
Returns number of keys in the database.
flags
$db->flags;
Returns flags passed as 4th argument to tie.
dbname
$db->dbname;
Returns the database name (i.e. 3rd argument to tie.
cache_size
$db->cache_size;
$db->cache_size($newsize);
Returns the size of the internal GDBM cache for that database.
Called with argument, sets the size to $newsize.
block_size
$db->block_size;
Returns the block size of the database.
sync_mode
$db->sync_mode;
$db->sync_mode($bool);
Returns the status of the automatic synchronization mode. Called with
argument, enables or disables the sync mode, depending on whether $bool
is true or false.
When synchronization mode is on (true), any changes to the database are
immediately written to the disk. This ensures database consistency in
case of any unforeseen errors (e.g. power failures), at the expense of
considerable slowdown of operation.
Synchronization mode is off by default.
centfree
$db->centfree;
$db->centfree($bool);
Returns status of the central free block pool (0 - disabled, 1 -
enabled).
With argument, changes its status.
By default, central free block pool is disabled.
coalesce
$db->coalesce;
$db->coalesce($bool);
mmap
$db->mmap;
Returns true if memory mapping is enabled.
This method will croak if the libgdbm library is complied without
memory mapping support.
mmapsize
$db->mmapsize;
$db->mmapsize($newsize);
If memory mapping is enabled, returns the size of memory mapping. With
argument, sets the size to $newsize.
This method will croak if the libgdbm library is complied without
memory mapping support.
recover
$db->recover(%args);
Recovers data from a failed database. %args is optional and can contain
following keys:
err => sub { ... }
Reference to code for detailed error reporting. Upon encountering
an error, recover will call this sub with a single argument - a
description of the error.
backup => \$str
Creates a backup copy of the database before recovery and returns
its filename in $str.
max_failed_keys => $n
Maximum allowed number of failed keys. If the actual number becomes
equal to $n, recover aborts and returns error.
max_failed_buckets => $n
Maximum allowed number of failed buckets. If the actual number
becomes equal to $n, recover aborts and returns error.
max_failures => $n
Maximum allowed number of failures during recovery.
stat => \%hash
Return recovery statistics in %hash. Upon return, the following
keys will be present:
recovered_keys
Number of successfully recovered keys.
recovered_buckets
Number of successfully recovered buckets.
failed_keys
Number of keys that failed to be retrieved.
failed_buckets
Number of buckets that failed to be retrieved.
AVAILABILITY
gdbm is available from any GNU archive. The master site is
"ftp.gnu.org", but you are strongly urged to use one of the many
mirrors. You can obtain a list of mirror sites from
<http://www.gnu.org/order/ftp.html>.
SECURITY AND PORTABILITY
Do not accept GDBM files from untrusted sources.
GDBM files are not portable across platforms.
The GDBM documentation doesn't imply that files from untrusted sources
can be safely used with "libgdbm".
A maliciously crafted file might cause perl to crash or even expose a
security vulnerability.
SEE ALSO
perl(1), DB_File(3), perldbmfilter, gdbm(3),
<https://www.gnu.org.ua/software/gdbm/manual.html>.
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