SDBM_File

Section: Perl Programmers Reference Guide (3)
Updated: 2001-09-21
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NAME

SDBM_File - Tied access to sdbm files

SYNOPSIS

 use Fcntl;   # For O_RDWR, O_CREAT, etc.
 use SDBM_File;

 tie(%h, 'SDBM_File', 'filename', O_RDWR|O_CREAT, 0666)
   or die "Couldn't tie SDBM file 'filename': $!; aborting";

 # Now read and change the hash
 $h{newkey} = newvalue;
 print $h{oldkey}; 
 ...

 untie %h;

DESCRIPTION

"SDBM_File" 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 runs.

Use "SDBM_File" with the Perl built-in "tie" function to establish the connection between the variable and the file. The arguments to "tie" should be:

1.

The hash variable you want to tie.

2.

The string "SDBM_File". (Ths tells Perl to use the "SDBM_File" package to perform the functions of the hash.)

3.

The name of the file you want to tie to the hash.

4.

Flags. Use one of:

O_RDONLY: Read-only access to the data in the file.
O_WRONLY: Write-only access to the data in the file.
O_RDWR: Both read and write access.

: If you want to create the file if it does not exist, add "O_CREAT" to any of these, as in the example. If you omit "O_CREAT" and the file does not already exist, the "tie" call will fail.

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 ``umask'' in perlfunc.)

DIAGNOSTICS

On failure, the "tie" call returns an undefined value and probably sets $! 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.

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.

See ``tie'' in perlfunc, perldbmfilter, Fcntl