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# SDBM_File

Perl 5 version 22.0 documentation
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# SDBM_File

- 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

Use `SDBM_File` with the Perl built-in `tie` 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 from File::Temp.

`$modeflags` can be the following constants from the `Fcntl` module (in the style of the open(2) system call),

        O_RDONLY          read-only access    O_WRONLY          write-only access    O_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 omit `O_CREAT` and the database does not already exist then the `tie` 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.)

# 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, 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, perldbmfilter, Fcntl

Page index

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