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.\" ========================================================================
.\"
.IX Title "SDBM_File 3"
.TH SDBM_File 3 "2019-05-11" "perl v5.30.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
SDBM_File \- Tied access to sdbm files
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\& use Fcntl; # For O_RDWR, O_CREAT, etc.
\& use SDBM_File;
\&
\& tie(%h, \*(AqSDBM_File\*(Aq, \*(Aqfilename\*(Aq, O_RDWR|O_CREAT, 0666)
\& or die "Couldn\*(Aqt tie SDBM file \*(Aqfilename\*(Aq: $!; aborting";
\&
\& # Now read and change the hash
\& $h{newkey} = newvalue;
\& print $h{oldkey};
\& ...
\&
\& untie %h;
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\f(CW\*(C`SDBM_File\*(C'\fR 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.
.SS "Tie"
.IX Subsection "Tie"
Use \f(CW\*(C`SDBM_File\*(C'\fR with the Perl built-in \f(CW\*(C`tie\*(C'\fR function to establish
the connection between the variable and the file.
.PP
.Vb 1
\& tie %hash, \*(AqSDBM_File\*(Aq, $basename, $modeflags, $perms;
\&
\& tie %hash, \*(AqSDBM_File\*(Aq, $dirfile, $modeflags, $perms, $pagfilename;
.Ve
.PP
\&\f(CW$basename\fR is the base filename for the database. The database is two
files with \*(L".dir\*(R" and \*(L".pag\*(R" extensions appended to \f(CW$basename\fR,
.PP
.Vb 2
\& $basename.dir (or .sdbm_dir on VMS, per DIRFEXT constant)
\& $basename.pag
.Ve
.PP
The two filenames can also be given separately in full as \f(CW$dirfile\fR
and \f(CW$pagfilename\fR. This suits for two files without \*(L".dir\*(R" and \*(L".pag\*(R"
extensions, perhaps for example two files from File::Temp.
.PP
\&\f(CW$modeflags\fR can be the following constants from the \f(CW\*(C`Fcntl\*(C'\fR module (in
the style of the \fBopen\fR\|(2) system call),
.PP
.Vb 3
\& O_RDONLY read\-only access
\& O_WRONLY write\-only access
\& O_RDWR read and write access
.Ve
.PP
If you want to create the file if it does not already exist then bitwise-OR
(\f(CW\*(C`|\*(C'\fR) \f(CW\*(C`O_CREAT\*(C'\fR too. If you omit \f(CW\*(C`O_CREAT\*(C'\fR and the database does not
already exist then the \f(CW\*(C`tie\*(C'\fR call will fail.
.PP
.Vb 1
\& O_CREAT create database if doesn\*(Aqt already exist
.Ve
.PP
\&\f(CW$perms\fR is the file permissions bits to use if new database files are
created. This parameter is mandatory even when not creating a new database.
The permissions will be reduced by the user's umask so the usual value here
would be 0666, or if some very private data then 0600. (See
\&\*(L"umask\*(R" in perlfunc.)
.SH "EXPORTS"
.IX Header "EXPORTS"
SDBM_File optionally exports the following constants:
.IP "\(bu" 4
\&\f(CW\*(C`PAGFEXT\*(C'\fR \- the extension used for the page file, usually \f(CW\*(C`.pag\*(C'\fR.
.IP "\(bu" 4
\&\f(CW\*(C`DIRFEXT\*(C'\fR \- the extension used for the directory file, \f(CW\*(C`.dir\*(C'\fR
everywhere but \s-1VMS,\s0 where it is \f(CW\*(C`.sdbm_dir\*(C'\fR.
.IP "\(bu" 4
\&\f(CW\*(C`PAIRMAX\*(C'\fR \- the maximum size of a stored hash entry, including the
length of both the key and value.
.PP
These constants can also be used with fully qualified names,
eg. \f(CW\*(C`SDBM_File::PAGFEXT\*(C'\fR.
.SH "DIAGNOSTICS"
.IX Header "DIAGNOSTICS"
On failure, the \f(CW\*(C`tie\*(C'\fR call returns an undefined value and probably
sets \f(CW$!\fR to contain the reason the file could not be tied.
.ie n .SS """sdbm store returned \-1, errno 22, key ""..."" at ..."""
.el .SS "\f(CWsdbm store returned \-1, errno 22, key ``...'' at ...\fP"
.IX Subsection "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 \s-1BUGS AND WARNINGS\s0 below.
.SH "SECURITY WARNING"
.IX Header "SECURITY WARNING"
\&\fBDo not accept \s-1SDBM\s0 files from untrusted sources!\fR
.PP
The sdbm file format was designed for speed and convenience, not for
portability or security. A maliciously crafted file might cause perl to
crash or even expose a security vulnerability.
.SH "BUGS AND WARNINGS"
.IX Header "BUGS AND WARNINGS"
There are a number of limits on the size of the data that you can
store in the \s-1SDBM\s0 file. The most important is that the length of a
key, plus the length of its associated value, may not exceed 1008
bytes.
.PP
See \*(L"tie\*(R" in perlfunc, perldbmfilter, Fcntl