AnyDBM_File

Section: Perl Programmers Reference Guide (3pm)
Updated: 2007-12-18
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NAME

AnyDBM_File - provide framework for multiple DBMs

NDBM_File, DB_File, GDBM_File, SDBM_File, ODBM_File - various DBM implementations  

SYNOPSIS

    use AnyDBM_File;
 

DESCRIPTION

This module is a ``pure virtual base class''--it has nothing of its own. It's just there to inherit from one of the various DBM packages. It prefers ndbm for compatibility reasons with Perl 4, then Berkeley DB (See DB_File), GDBM, SDBM (which is always there---it comes with Perl), and finally ODBM. This way old programs that used to use NDBM via dbmopen() can still do so, but new ones can reorder @ISA: 

    BEGIN { @AnyDBM_File::ISA = qw(DB_File GDBM_File NDBM_File) }
    use AnyDBM_File;

Having multiple DBM implementations makes it trivial to copy database formats: 

    use POSIX; use NDBM_File; use DB_File;
    tie %newhash,  'DB_File', $new_filename, O_CREAT|O_RDWR;
    tie %oldhash,  'NDBM_File', $old_filename, 1, 0;
    %newhash = %oldhash;
 

DBM Comparisons

Here's a partial table of features the different packages offer: 

                         odbm    ndbm    sdbm    gdbm    bsd-db
                         ----    ----    ----    ----    ------
 Linkage comes w/ perl   yes     yes     yes     yes     yes
 Src comes w/ perl       no      no      yes     no      no
 Comes w/ many unix os   yes     yes[0]  no      no      no
 Builds ok on !unix      ?       ?       yes     yes     ?
 Code Size               ?       ?       small   big     big
 Database Size           ?       ?       small   big?    ok[1]
 Speed                   ?       ?       slow    ok      fast
 FTPable                 no      no      yes     yes     yes
 Easy to build          N/A     N/A      yes     yes     ok[2]
 Size limits             1k      4k      1k[3]   none    none
 Byte-order independent  no      no      no      no      yes
 Licensing restrictions  ?       ?       no      yes     no
[0]
on mixed universe machines, may be in the bsd compat library, which is often shunned.
[1]
Can be trimmed if you compile for one access method.
[2]
See DB_File. Requires symbolic links.
[3]
By default, but can be redefined.
 

SEE ALSO

dbm(3), ndbm(3), DB_File(3), perldbmfilter