1ODBM_File(3pm)         Perl Programmers Reference Guide         ODBM_File(3pm)
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NAME

6       ODBM_File - Tied access to odbm files
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SYNOPSIS

9        use Fcntl;   # For O_RDWR, O_CREAT, etc.
10        use ODBM_File;
11
12         # Now read and change the hash
13         $h{newkey} = newvalue;
14         print $h{oldkey};
15         ...
16
17         untie %h;
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DESCRIPTION

20       "ODBM_File" establishes a connection between a Perl hash variable and a
21       file in ODBM_File format;.  You can manipulate the data in the file
22       just as if it were in a Perl hash, but when your program exits, the
23       data will remain in the file, to be used the next time your program
24       runs.
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26       Use "ODBM_File" with the Perl built-in "tie" function to establish the
27       connection between the variable and the file.  The arguments to "tie"
28       should be:
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30       1.  The hash variable you want to tie.
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32       2.  The string "ODBM_File".  (Ths tells Perl to use the "ODBM_File"
33           package to perform the functions of the hash.)
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35       3.  The name of the file you want to tie to the hash.
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37       4.  Flags.  Use one of:
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39           "O_RDONLY"
40             Read-only access to the data in the file.
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42           "O_WRONLY"
43             Write-only access to the data in the file.
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45           "O_RDWR"
46             Both read and write access.
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48           If you want to create the file if it does not exist, add "O_CREAT"
49           to any of these, as in the example.  If you omit "O_CREAT" and the
50           file does not already exist, the "tie" call will fail.
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52       5.  The default permissions to use if a new file is created.  The
53           actual permissions will be modified by the user's umask, so you
54           should probably use 0666 here. (See "umask" in perlfunc.)
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DIAGNOSTICS

57       On failure, the "tie" call returns an undefined value and probably sets
58       $! to contain the reason the file could not be tied.
59
60   "odbm store returned -1, errno 22, key "..." at ..."
61       This warning is emitted when you try to store a key or a value that is
62       too long.  It means that the change was not recorded in the database.
63       See BUGS AND WARNINGS below.
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SECURITY AND PORTABILITY

66       Do not accept ODBM files from untrusted sources.
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68       On modern Linux systems these are typically GDBM files, which are not
69       portable across platforms.
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71       The GDBM documentation doesn't imply that files from untrusted sources
72       can be safely used with "libgdbm".
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74       Systems that don't use GDBM compatibilty for old dbm support will be
75       using a platform specific library, possibly inherited from BSD systems,
76       where it may or may not be safe to use an untrusted file.
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78       A maliciously crafted file might cause perl to crash or even expose a
79       security vulnerability.
80

BUGS AND WARNINGS

82       There are a number of limits on the size of the data that you can store
83       in the ODBM file.  The most important is that the length of a key, plus
84       the length of its associated value, may not exceed 1008 bytes.
85
86       See "tie" in perlfunc, perldbmfilter, Fcntl
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90perl v5.30.2                      2020-03-27                    ODBM_File(3pm)
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