Perl 5 version 30.0 documentation
- SECURITY WARNING
- BUGS AND WARNINGS
SDBM_File - Tied access to sdbm files
establishes a connection between a Perl hash variable and
a file in SDBM_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
with the Perl built-in
tie function to establish
the connection between the variable and the file.
is the base filename for the database. The database is two
files with ".dir" and ".pag" extensions appended to
- $basename.dir (or .sdbm_dir on VMS, per DIRFEXT constant)
The two filenames can also be given separately in full as
. This suits for two files without ".dir" and ".pag"
extensions, perhaps for example two files from File::Temp.
can be the following constants from the
the style of the open(2) system call),
If you want to create the file if it does not already exist then bitwise-OR
too. If you omit
and the database does not
already exist then the
tie call will fail.
- O_CREAT create database if doesn't already exist
is the file permissions bits to use if new database files are
created. This parameter is mandatory even when not creating a new database.
The permissions will be reduced by the user's umask so the usual value here
would be 0666, or if some very private data then 0600. (See
SDBM_File optionally exports the following constants:
PAGFEXT- the extension used for the page file, usually
DIRFEXT- the extension used for the directory file,
.direverywhere but VMS, where it is
PAIRMAX- the maximum size of a stored hash entry, including the length of both the key and value.
These constants can also be used with fully qualified names,
On failure, the
tie call returns an undefined value and probably
to contain the reason the file could not be tied.
sdbm 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.
Do not accept SDBM files from untrusted sources!
The sdbm file format was designed for speed and convenience, not for portability or security. A maliciously crafted file might cause perl to crash or even expose a security vulnerability.
BUGS AND WARNINGS
There are a number of limits on the size of the data that you can store in the SDBM file. The most important is that the length of a key, plus the length of its associated value, may not exceed 1008 bytes.