SDBM_File documentation

[perl5.git] / ext / SDBM_File / SDBM_File.pm

diff --git a/ext/SDBM_File/SDBM_File.pm b/ext/SDBM_File/SDBM_File.pm
index c5e26c8..438b8d0 100644 (file)
--- a/ext/SDBM_File/SDBM_File.pm
+++ b/ext/SDBM_File/SDBM_File.pm
@@ -20,14 +20,98 @@ SDBM_File - Tied access to sdbm files
 
 =head1 SYNOPSIS
 
+ use Fcntl;   # For O_RDWR, O_CREAT, etc.
  use SDBM_File;
 
- tie(%h, 'SDBM_File', 'Op.dbmx', O_RDWR|O_CREAT, 0640);
+ 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;
 
 =head1 DESCRIPTION
 
-See L<perlfunc/tie>, L<perldbmfilter>
+C<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 C<SDBM_File> with the Perl built-in C<tie> function to establish
+the connection between the variable and the file.  The arguments to
+C<tie> should be:
+
+=over 4
+
+=item 1.
+
+The hash variable you want to tie.
+
+=item 2. 
+
+The string C<"SDBM_File">.  (Ths tells Perl to use the C<SDBM_File>
+package to perform the functions of the hash.)
+
+=item 3. 
+
+The name of the file you want to tie to the hash.  
+
+=item 4.
+
+Flags.  Use one of:
+
+=over 2
+
+=item C<O_RDONLY>
+
+Read-only access to the data in the file.
+
+=item C<O_WRONLY>
+
+Write-only access to the data in the file.
+
+=item C<O_RDWR>
+
+Both read and write access.
+
+=back
+
+If you want to create the file if it does not exist, add C<O_CREAT> to
+any of these, as in the example.  If you omit C<O_CREAT> and the file
+does not already exist, the C<tie> call will fail.
+
+=item 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 L<perlfunc/umask>.)
+
+=back
+
+=head1 DIAGNOSTICS
+
+On failure, the C<tie> call returns an undefined value and probably
+sets C<$!> to contain the reason the file could not be tied.
+
+=head2 C<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.
+
+
+
+=head1 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 L<perlfunc/tie>, L<perldbmfilter>, L<Fcntl>
 
 =cut