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GNU/Linux |
CentOS 5.3 |
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SDBM_File(3pm) |
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SDBM_File − Tied access to sdbm files
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;
"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:
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1. |
The hash variable you want to tie. | ||
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2. |
The string "SDBM_File". (Ths tells Perl to use the "SDBM_File" package to perform the functions of the hash.) | ||
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3. |
The name of the file you want to tie to the hash. | ||
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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.
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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.) |
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.
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
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SDBM_File(3pm) | |