SDBM_File(3pm) Perl Programmers Reference Guide SDBM_File(3pm)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.
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.
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 "umask" in perlfunc.)
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" in perlfunc, perldbmfilter, Fcntl
perl v5.12.5 2012-11-03 SDBM_File(3pm)
