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DBD::CSV(3pm)         User Contributed Perl Documentation        DBD::CSV(3pm)

NAME
       DBD::CSV - DBI driver for CSV files

SYNOPSIS
           use DBI;
           # See "Creating database handle" below
           $dbh = DBI->connect ("dbi:CSV:", undef, undef, {
               f_ext      => ".csv/r",
               RaiseError => 1,
               }) or die "Cannot connect: $DBI::errstr";

           # Simple statements
           $dbh->do ("CREATE TABLE foo (id INTEGER, name CHAR (10))");

           # Selecting
           my $sth = $dbh->prepare ("select * from foo");
           $sth->execute;
           $sth->bind_columns (\my ($id, $name));
           while ($sth->fetch) {
               print "id: $id, name: $name\n";
               }

           # Updates
           my $sth = $dbh->prepare ("UPDATE foo SET name = ? WHERE id = ?");
           $sth->execute ("DBI rocks!", 1);
           $sth->finish;

           $dbh->disconnect;

DESCRIPTION
       The DBD::CSV module is yet another driver for the DBI (Database
       independent interface for Perl). This one is based on the SQL "engine"
       SQL::Statement and the abstract DBI driver DBD::File and implements
       access to so-called CSV files (Comma Separated Values). Such files are
       often used for exporting MS Access and MS Excel data.

       See DBI for details on DBI, SQL::Statement for details on
       SQL::Statement and DBD::File for details on the base class DBD::File.

   Prerequisites
       The only system dependent feature that DBD::File uses, is the "flock
       ()" function. Thus the module should run (in theory) on any system with
       a working "flock ()", in particular on all Unix machines and on Windows
       NT. Under Windows 95 and MacOS the use of "flock ()" is disabled, thus
       the module should still be usable.

       Unlike other DBI drivers, you don't need an external SQL engine or a
       running server. All you need are the following Perl modules, available
       from any CPAN mirror, for example

         http://search.cpan.org/

       DBI A recent version of the DBI (Database independent interface for
           Perl).  See below why.

       DBD::File
           This is the base class for DBD::CSV, and it is part of the DBI
           distribution. As DBD::CSV requires a matching version of DBD::File
           which is (partly) developed by the same team that maintains
           DBD::CSV. See META.json or Makefile.PL for the minimum versions.

       SQL::Statement
           A simple SQL engine. This module defines all of the SQL syntax for
           DBD::CSV, new SQL support is added with each release so you should
           look for updates to SQL::Statement regularly.

           It is possible to run "DBD::CSV" without this module if you define
           the environment variable $DBI_SQL_NANO to 1. This will reduce the
           SQL support a lot though. See DBI::SQL::Nano for more details. Note
           that the test suite does only test in this mode in the development
           environment.

       Text::CSV_XS
           This module is used to read and write rows in a CSV file.

   Installation
       Installing this module (and the prerequisites from above) is quite
       simple.  The simplest way is to install the bundle:

           $ cpan Bundle::DBD::CSV

       Alternatively, you can name them all

           $ cpan Text::CSV_XS DBI DBD::CSV

       or even trust "cpan" to resolve all dependencies for you:

           $ cpan DBD::CSV

       If you cannot, for whatever reason, use cpan, fetch all modules from
       CPAN, and build with a sequence like:

           gzip -d < DBD-CSV-0.40.tgz | tar xf -

       (this is for Unix users, Windows users would prefer WinZip or something
       similar) and then enter the following:

           cd DBD-CSV-0.40
           perl Makefile.PL
           make test

       If any tests fail, let us know. Otherwise go on with

           make install UNINST=1

       Note that you almost definitely need root or administrator permissions.
       If you don't have them, read the ExtUtils::MakeMaker man page for
       details on installing in your own directories. ExtUtils::MakeMaker.

   Supported SQL Syntax
       All SQL processing for DBD::CSV is done by SQL::Statement. See
       SQL::Statement for more specific information about its feature set.
       Features include joins, aliases, built-in and user-defined functions,
       and more.  See SQL::Statement::Syntax for a description of the SQL
       syntax supported in DBD::CSV.

       Table- and column-names are case insensitive unless quoted. Column
       names will be sanitized unless "raw_header" is true.

Using DBD::CSV with DBI
       For most things, DBD-CSV operates the same as any DBI driver.  See DBI
       for detailed usage.

   Creating a database handle (connect)
       Creating a database handle usually implies connecting to a database
       server.  Thus this command reads

           use DBI;
           my $dbh = DBI->connect ("dbi:CSV:", "", "", {
               f_dir => "/home/user/folder",
               });

       The directory tells the driver where it should create or open tables
       (a.k.a.  files). It defaults to the current directory, so the following
       are equivalent:

           $dbh = DBI->connect ("dbi:CSV:");
           $dbh = DBI->connect ("dbi:CSV:", undef, undef, { f_dir => "." });
           $dbh = DBI->connect ("dbi:CSV:f_dir=.");

       We were told, that VMS might - for whatever reason - require:

           $dbh = DBI->connect ("dbi:CSV:f_dir=");

       The preferred way of passing the arguments is by driver attributes:

           # specify most possible flags via driver flags
           $dbh = DBI->connect ("dbi:CSV:", undef, undef, {
               f_schema         => undef,
               f_dir            => "data",
               f_dir_search     => [],
               f_ext            => ".csv/r",
               f_lock           => 2,
               f_encoding       => "utf8",

               csv_eol          => "\r\n",
               csv_sep_char     => ",",
               csv_quote_char   => '"',
               csv_escape_char  => '"',
               csv_class        => "Text::CSV_XS",
               csv_null         => 1,
               csv_bom          => 0,
               csv_tables       => {
                   syspwd => {
                       sep_char    => ":",
                       quote_char  => undef,
                       escape_char => undef,
                       file        => "/etc/passwd",
                       col_names   => [qw( login password
                                           uid gid realname
                                           directory shell )],
                       },
                   },

               RaiseError       => 1,
               PrintError       => 1,
               FetchHashKeyName => "NAME_lc",
               }) or die $DBI::errstr;

       but you may set these attributes in the DSN as well, separated by
       semicolons.  Pay attention to the semi-colon for "csv_sep_char" (as
       seen in many CSV exports from MS Excel) is being escaped in below
       example, as is would otherwise be seen as attribute separator:

           $dbh = DBI->connect (
               "dbi:CSV:f_dir=$ENV{HOME}/csvdb;f_ext=.csv;f_lock=2;" .
               "f_encoding=utf8;csv_eol=\n;csv_sep_char=\\;;" .
               "csv_quote_char=\";csv_escape_char=\\;csv_class=Text::CSV_XS;" .
               "csv_null=1") or die $DBI::errstr;

       Using attributes in the DSN is easier to use when the DSN is derived
       from an outside source (environment variable, database entry, or
       configure file), whereas specifying entries in the attribute hash is
       easier to read and to maintain.

       The default value for "csv_binary" is 1 (True).

       The default value for "csv_auto_diag" is <1>. Note that this might
       cause trouble on perl versions older than 5.8.9, so up to and including
       perl version 5.8.8 it might be required to use ";csv_auto_diag=0"
       inside the "DSN" or "csv_auto_diag =" 0> inside the attributes.

   Creating and dropping tables
       You can create and drop tables with commands like the following:

           $dbh->do ("CREATE TABLE $table (id INTEGER, name CHAR (64))");
           $dbh->do ("DROP TABLE $table");

       Note that currently only the column names will be stored and no other
       data.  Thus all other information including column type (INTEGER or
       CHAR (x), for example), column attributes (NOT NULL, PRIMARY KEY, ...)
       will silently be discarded. This may change in a later release.

       A drop just removes the file without any warning.

       See DBI for more details.

       Table names cannot be arbitrary, due to restrictions of the SQL syntax.
       I recommend that table names are valid SQL identifiers: The first
       character is alphabetic, followed by an arbitrary number of
       alphanumeric characters. If you want to use other files, the file names
       must start with "/", "./" or "../" and they must not contain white
       space.

   Inserting, fetching and modifying data
       The following examples insert some data in a table and fetch it back:
       First, an example where the column data is concatenated in the SQL
       string:

           $dbh->do ("INSERT INTO $table VALUES (1, ".
                      $dbh->quote ("foobar") . ")");

       Note the use of the quote method for escaping the word "foobar". Any
       string must be escaped, even if it does not contain binary data.

       Next, an example using parameters:

           $dbh->do ("INSERT INTO $table VALUES (?, ?)", undef, 2,
                     "It's a string!");

       Note that you don't need to quote column data passed as parameters.
       This version is particularly well designed for loops. Whenever
       performance is an issue, I recommend using this method.

       You might wonder about the "undef". Don't wonder, just take it as it
       is. :-) It's an attribute argument that I have never used and will be
       passed to the prepare method as the second argument.

       To retrieve data, you can use the following:

           my $query = "SELECT * FROM $table WHERE id > 1 ORDER BY id";
           my $sth   = $dbh->prepare ($query);
           $sth->execute ();
           while (my $row = $sth->fetchrow_hashref) {
               print "Found result row: id = ", $row->{id},
                     ", name = ", $row->{name};
               }
           $sth->finish ();

       Again, column binding works: The same example again.

           my $sth = $dbh->prepare (qq;
               SELECT * FROM $table WHERE id > 1 ORDER BY id;
               ;);
           $sth->execute;
           my ($id, $name);
           $sth->bind_columns (undef, \$id, \$name);
           while ($sth->fetch) {
               print "Found result row: id = $id, name = $name\n";
               }
           $sth->finish;

       Of course you can even use input parameters. Here's the same example
       for the third time:

           my $sth = $dbh->prepare ("SELECT * FROM $table WHERE id = ?");
           $sth->bind_columns (undef, \$id, \$name);
           for (my $i = 1; $i <= 2; $i++) {
               $sth->execute ($id);
               if ($sth->fetch) {
                   print "Found result row: id = $id, name = $name\n";
                   }
               $sth->finish;
               }

       See DBI for details on these methods. See SQL::Statement for details on
       the WHERE clause.

       Data rows are modified with the UPDATE statement:

           $dbh->do ("UPDATE $table SET id = 3 WHERE id = 1");

       Likewise you use the DELETE statement for removing rows:

           $dbh->do ("DELETE FROM $table WHERE id > 1");

   Error handling
       In the above examples we have never cared about return codes. Of
       course, this is not recommended. Instead we should have written (for
       example):

           my $sth = $dbh->prepare ("SELECT * FROM $table WHERE id = ?") or
               die "prepare: " . $dbh->errstr ();
           $sth->bind_columns (undef, \$id, \$name) or
               die "bind_columns: " . $dbh->errstr ();
           for (my $i = 1; $i <= 2; $i++) {
               $sth->execute ($id) or
                   die "execute: " . $dbh->errstr ();
               $sth->fetch and
                   print "Found result row: id = $id, name = $name\n";
               }
           $sth->finish ($id) or die "finish: " . $dbh->errstr ();

       Obviously this is tedious. Fortunately we have DBI's RaiseError
       attribute:

           $dbh->{RaiseError} = 1;
           $@ = "";
           eval {
               my $sth = $dbh->prepare ("SELECT * FROM $table WHERE id = ?");
               $sth->bind_columns (undef, \$id, \$name);
               for (my $i = 1; $i <= 2; $i++) {
                   $sth->execute ($id);
                   $sth->fetch and
                       print "Found result row: id = $id, name = $name\n";
                   }
               $sth->finish ($id);
               };
           $@ and die "SQL database error: $@";

       This is not only shorter, it even works when using DBI methods within
       subroutines.

DBI database handle attributes
   Metadata
       The following attributes are handled by DBI itself and not by
       DBD::File, thus they all work as expected:

           Active
           ActiveKids
           CachedKids
           CompatMode             (Not used)
           InactiveDestroy
           Kids
           PrintError
           RaiseError
           Warn                   (Not used)

       The following DBI attributes are handled by DBD::File:

       AutoCommit
           Always on

       ChopBlanks
           Works

       NUM_OF_FIELDS
           Valid after "$sth->execute"

       NUM_OF_PARAMS
           Valid after "$sth->prepare"

       NAME
       NAME_lc
       NAME_uc
           Valid after "$sth->execute"; undef for Non-Select statements.

       NULLABLE
           Not really working. Always returns an array ref of one's, as
           DBD::CSV does not verify input data. Valid after "$sth->execute";
           undef for non-Select statements.

       These attributes and methods are not supported:

           bind_param_inout
           CursorName
           LongReadLen
           LongTruncOk

DBD-CSV specific database handle attributes
       In addition to the DBI attributes, you can use the following dbh
       attributes:

   DBD::File attributes
       f_dir
           This attribute is used for setting the directory where CSV files
           are opened. Usually you set it in the dbh and it defaults to the
           current directory ("."). However, it may be overridden in statement
           handles.

       f_dir_search
           This attribute optionally defines a list of extra directories to
           search when opening existing tables. It should be an anonymous list
           or an array reference listing all folders where tables could be
           found.

               my $dbh = DBI->connect ("dbi:CSV:", "", "", {
                   f_dir        => "data",
                   f_dir_search => [ "ref/data", "ref/old" ],
                   f_ext        => ".csv/r",
                   }) or die $DBI::errstr;

       f_ext
           This attribute is used for setting the file extension.

       f_schema
           This attribute allows you to set the database schema name. The
           default is to use the owner of "f_dir". "undef" is allowed, but not
           in the DSN part.

               my $dbh = DBI->connect ("dbi:CSV:", "", "", {
                   f_schema => undef,
                   f_dir    => "data",
                   f_ext    => ".csv/r",
                   }) or die $DBI::errstr;

       f_encoding
           This attribute allows you to set the encoding of the data. With
           CSV, it is not possible to set (and remember) the encoding on a
           column basis, but DBD::File now allows the encoding to be set on
           the underlying file. If this attribute is not set, or undef is
           passed, the file will be seen as binary.

       f_lock
           With this attribute you can specify a locking mode to be used (if
           locking is supported at all) for opening tables. By default, tables
           are opened with a shared lock for reading, and with an exclusive
           lock for writing. The supported modes are:

           0 Force no locking at all.

           1 Only shared locks will be used.

           2 Only exclusive locks will be used.

       But see "KNOWN BUGS" in DBD::File.

   DBD::CSV specific attributes
       csv_class
           The attribute csv_class controls the CSV parsing engine. This
           defaults to "Text::CSV_XS", but "Text::CSV" can be used in some
           cases, too.  Please be aware that "Text::CSV" does not care about
           any edge case as "Text::CSV_XS" does and that "Text::CSV" is
           probably about 100 times slower than "Text::CSV_XS".

           In order to use the specified class other than "Text::CSV_XS", it
           needs to be loaded before use.  "DBD::CSV" does not "require"/"use"
           the specified class itself.

   Text::CSV_XS specific attributes
       csv_eol
       csv_sep_char
       csv_quote_char
       csv_escape_char
       csv_csv
           The attributes csv_eol, csv_sep_char, csv_quote_char and
           csv_escape_char are corresponding to the respective attributes of
           the csv_class (usually Text::CSV_CS) object. You may want to set
           these attributes if you have unusual CSV files like /etc/passwd or
           MS Excel generated CSV files with a semicolon as separator.
           Defaults are "\015\012"", ",", """ and """, respectively.

           The csv_eol attribute defines the end-of-line pattern, which is
           better known as a record separator pattern since it separates
           records.  The default is windows-style end-of-lines "\015\012" for
           output (writing) and unset for input (reading), so if on unix you
           may want to set this to newline ("\n") like this:

             $dbh->{csv_eol} = "\n";

           It is also possible to use multi-character patterns as record
           separators.  For example this file uses newlines as field
           separators (sep_char) and the pattern "\n__ENDREC__\n" as the
           record separators (eol):

             name
             city
             __ENDREC__
             joe
             seattle
             __ENDREC__
             sue
             portland
             __ENDREC__

           To handle this file, you'd do this:

             $dbh->{eol}      = "\n__ENDREC__\n" ,
             $dbh->{sep_char} = "\n"

           The attributes are used to create an instance of the class
           csv_class, by default Text::CSV_XS. Alternatively you may pass an
           instance as csv_csv, the latter takes precedence. Note that the
           binary attribute must be set to a true value in that case.

           Additionally you may overwrite these attributes on a per-table base
           in the csv_tables attribute.

       csv_null
           With this option set, all new statement handles will set
           "always_quote" and "blank_is_undef" in the CSV parser and writer,
           so it knows how to distinguish between the empty string and "undef"
           or "NULL". You cannot reset it with a false value. You can pass it
           to connect, or set it later:

             $dbh = DBI->connect ("dbi:CSV:", "", "", { csv_null => 1 });

             $dbh->{csv_null} = 1;

       csv_bom
           With this option set, the CSV parser will try to detect BOM (Byte
           Order Mark) in the header line. This requires Text::CSV_XS version
           1.22 or higher.

             $dbh = DBI->connect ("dbi:CSV:", "", "", { csv_bom => 1 });

             $dbh->{csv_bom} = 1;

       csv_tables
           This hash ref is used for storing table dependent metadata. For any
           table it contains an element with the table name as key and another
           hash ref with the following attributes:

           o   All valid attributes to the CSV parsing module. Any of them can
               optionally be prefixed with "csv_".

           o   All attributes valid to DBD::File

           If you pass it "f_file" or its alias "file", "f_ext" has no effect,
           but "f_dir" and "f_encoding" still have.

             csv_tables => {
                 syspwd => {                   # Table name
                     csv_sep_char => ":",      # Text::CSV_XS
                     quote_char   => undef,    # Text::CSV_XS
                     escape_char  => undef,    # Text::CSV_XS
                     f_dir        => "/etc",   # DBD::File
                     f_file       => "passwd", # DBD::File
                     col_names    =>           # DBD::File
                       [qw( login password uid gid realname directory shell )],
                     },
                 },

       csv_*
           All other attributes that start with "csv_" and are not described
           above will be passed to "Text::CSV_XS" (without the "csv_" prefix).
           These extra options are only likely to be useful for reading
           (select) handles. Examples:

             $dbh->{csv_allow_whitespace}    = 1;
             $dbh->{csv_allow_loose_quotes}  = 1;
             $dbh->{csv_allow_loose_escapes} = 1;

           See the "Text::CSV_XS" documentation for the full list and the
           documentation.

   Driver specific attributes
       f_file
           The name of the file used for the table; defaults to

               "$dbh->{f_dir}/$table"

       eol
       sep_char
       quote_char
       escape_char
       class
       csv These correspond to the attributes csv_eol, csv_sep_char,
           csv_quote_char, csv_escape_char, csv_class and csv_csv.  The
           difference is that they work on a per-table basis.

       col_names
       skip_first_row
           By default DBD::CSV assumes that column names are stored in the
           first row of the CSV file and sanitizes them (see "raw_header"
           below). If this is not the case, you can supply an array ref of
           table names with the col_names attribute. In that case the
           attribute skip_first_row will be set to FALSE.

           If you supply an empty array ref, the driver will read the first
           row for you, count the number of columns and create column names
           like "col0", "col1", ...

           Note that column names that match reserved SQL words will cause
           unwanted and sometimes confusing errors. If your CSV has headers
           that match reserved words, you will require these two attributes.

           If "test.csv" looks like

            select,from
            1,2

           the select query would result in "select select, from from test;",
           which obviously is illegal SQL.

       raw_header
           Due to the SQL standard, field names cannot contain special
           characters like a dot (".") or a space (" ") unless the column
           names are quoted.  Following the approach of mdb_tools, all these
           tokens are translated to an underscore ("_") when reading the first
           line of the CSV file, so all field names are 'sanitized'. If you do
           not want this to happen, set "raw_header" to a true value and the
           entries in the first line of the CSV data will be used verbatim for
           column headers and field names.  DBD::CSV cannot guarantee that any
           part in the toolchain will work if field names have those
           characters, and the chances are high that the SQL statements will
           fail.

           Currently, the sanitizing of headers is as simple as

             s/\W/_/g;

           Note that headers (column names) might be folded in other parts of
           the code stack, specifically SQL::Statement, whose docs mention:

            Wildcards are expanded to lower cased identifiers. This might
            confuse some people, but it was easier to implement.

           That means that in

            my $sth = $dbh->prepare ("select * from foo");
            $sth->execute;
            while (my $row = $sth->fetchrow_hashref) {
                say for keys %$row;
                }

           all keys will show as all lower case, regardless of the original
           header.

       It's strongly recommended to check the attributes supported by
       "Metadata" in DBD::File.

       Example: Suppose you want to use /etc/passwd as a CSV file. :-) There
       simplest way is:

           use DBI;
           my $dbh = DBI->connect ("dbi:CSV:", undef, undef, {
               f_dir           => "/etc",
               csv_sep_char    => ":",
               csv_quote_char  => undef,
               csv_escape_char => undef,
               });
           $dbh->{csv_tables}{passwd} = {
               col_names => [qw( login password uid gid realname
                                 directory shell )];
               };
           $sth = $dbh->prepare ("SELECT * FROM passwd");

       Another possibility where you leave all the defaults as they are and
       override them on a per table basis:

           require DBI;
           my $dbh = DBI->connect ("dbi:CSV:");
           $dbh->{csv_tables}{passwd} = {
               eol         => "\n",
               sep_char    => ":",
               quote_char  => undef,
               escape_char => undef,
               f_file      => "/etc/passwd",
               col_names   => [qw( login password uid gid
                                   realname directory shell )],
               };
           $sth = $dbh->prepare ("SELECT * FROM passwd");

   Driver private methods
       These methods are inherited from DBD::File:

       data_sources
           The "data_sources" method returns a list of sub-directories of the
           current directory in the form "dbi:CSV:directory=$dirname".

           If you want to read the sub-directories of another directory, use

               my $drh  = DBI->install_driver ("CSV");
               my @list = $drh->data_sources (f_dir => "/usr/local/csv_data");

       list_tables
           This method returns a list of file-names inside $dbh->{directory}.
           Example:

               my $dbh  = DBI->connect ("dbi:CSV:directory=/usr/local/csv_data");
               my @list = $dbh->func ("list_tables");

           Note that the list includes all files contained in the directory,
           even those that have non-valid table names, from the view of SQL.
           See "Creating and dropping tables" above.

KNOWN ISSUES
       o   The module is using flock () internally. However, this function is
           not available on some platforms. Use of flock () is disabled on
           MacOS and Windows 95: There's no locking at all (perhaps not so
           important on these operating systems, as they are for single users
           anyways).

TODO
       Tests
           Aim for a full 100% code coverage

            - eol      Make tests for different record separators.
            - csv_xs   Test with a variety of combinations for
                       sep_char, quote_char, and escape_char testing
            - quoting  $dbh->do ("drop table $_") for DBI-tables ();
            - errors   Make sure that all documented exceptions are tested.
                       . write to write-protected file
                       . read from badly formatted csv
                       . pass bad arguments to csv parser while fetching

           Add tests that specifically test DBD::File functionality where that
           is useful.

       RT  Attack all open DBD::CSV bugs in RT

       CPAN::Forum
           Attack all items in http://www.cpanforum.com/dist/DBD-CSV

       Documentation
           Expand on error-handling, and document all possible errors.  Use
           Text::CSV_XS::error_diag () wherever possible.

       Debugging
           Implement and document dbd_verbose.

       Data dictionary
           Investigate the possibility to store the data dictionary in a file
           like .sys$columns that can store the field attributes (type, key,
           nullable).

       Examples
           Make more real-life examples from the docs in examples/

SEE ALSO
       DBI, Text::CSV_XS, SQL::Statement, DBI::SQL::Nano

       For help on the use of DBD::CSV, see the DBI users mailing list:

         http://lists.cpan.org/showlist.cgi?name=dbi-users

       For general information on DBI see

         http://dbi.perl.org/ and http://faq.dbi-support.com/

AUTHORS and MAINTAINERS
       This module is currently maintained by

           H.Merijn Brand <h.m.brand AT xs4all.nl>

       in close cooperation with and help from

           Jens Rehsack <sno AT NetBSD.org>

       The original author is Jochen Wiedmann.  Previous maintainer was Jeff
       Zucker

COPYRIGHT AND LICENSE
       Copyright (C) 2009-2021 by H.Merijn Brand Copyright (C) 2004-2009 by
       Jeff Zucker Copyright (C) 1998-2004 by Jochen Wiedmann

       All rights reserved.

       You may distribute this module under the terms of either the GNU
       General Public License or the Artistic License, as specified in the
       Perl README file.

perl v5.32.1                      2021-02-13                     DBD::CSV(3pm)