


SDBM_File(3p)    Perl Programmers Reference Guide   SDBM_File(3p)


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 manipu-
       late 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.





2001-05-24                 perl v5.6.1                          1





SDBM_File(3p)    Perl Programmers Reference Guide   SDBM_File(3p)


       5.  The default permissions to use if a new file is cre-
           ated.  The actual permissions will be modified by the
           user's umask, so you should probably use 0666 here.
           (See the umask entry in the perlfunc manpage.)

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 emmitted 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 associ-
       ated value, may not exceed 1008 bytes.

       See the tie entry in the perlfunc manpage, the perldbmfil-
       ter manpage, the Fcntl manpage

































2001-05-24                 perl v5.6.1                          2


