CONTENTS

• NAME
• SYNOPSIS
• DESCRIPTION
  • Tie
• EXPORTS
• DIAGNOSTICS
  • sdbm store returned -1, errno 22, key "..." at ...
• BUGS AND WARNINGS

#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.

#Tie

UseSDBM_File with the Perl built-intie function to establish the connection between the variable and the file.

tie %hash, 'SDBM_File', $basename, $modeflags, $perms;tie %hash, 'SDBM_File', $dirfile,  $modeflags, $perms, $pagfilename;

$basename is the base filename for the database. The database is two files with ".dir" and ".pag" extensions appended to$basename,

$basename.dir     (or .sdbm_dir on VMS, per DIRFEXT constant)$basename.pag

The two filenames can also be given separately in full as$dirfile and$pagfilename. This suits for two files without ".dir" and ".pag" extensions, perhaps for example two files fromFile::Temp.

$modeflags can be the following constants from theFcntl module (in the style of theopen(2) system call),

O_RDONLY          read-only accessO_WRONLY          write-only accessO_RDWR            read and write access

If you want to create the file if it does not already exist then bitwise-OR (|)O_CREAT too. If you omitO_CREAT and the database does not already exist then thetie call will fail.

O_CREAT           create database if doesn't already exist

$perms 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"umask" in perlfunc.)

#EXPORTS

SDBM_File optionally exports the following constants:

• PAGFEXT - the extension used for the page file, usually.pag.

• DIRFEXT - the extension used for the directory file,.dir everywhere but VMS, where it is.sdbm_dir.

• 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, eg.SDBM_File::PAGFEXT.

#DIAGNOSTICS

On failure, thetie 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

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