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To get around this particular problem, you need to investigate a system that automatically handles the indexing and searching of your database in a timely manner but still provides you with a simple interface for extracting the individual records and fields from the database files The easiest solution is to use the DBM system (the precise expansion of the acronym has been lost, but it probably stands for database management) This is a hashing database using the same key/value pair system as Perl s internal hash variable The more complex database implementations, especially those relying on relational features, either require more complex use of the text or DBM database systems or require the use of an external database implementation Perl supports access to all of the major database systems and many of the smaller systems, through a number of extensions provided through the DBI toolkit, a third-party module available from CPAN Using a series of database drivers (DBDs), the DBI toolkit allows you to create and use databases using Oracle, Sybase, mSQL/mySQL, PostgreSQL, and ODBC (open database connectivity) Under Windows you can use either the DBI interfaces or the Win32::ODBC toolkit, which provides direct access to any ODBC-compliant database, including FileMaker Pro, Oracle, and Microsoft s Visual FoxPro, Access, and SQL Server database products In this chapter, we ll look at all four solutions text, DBM, DBI, and ODBC and at more general methods and practices for creating and using databases within Perl We ll also look at ways of using DBM databases for storing complex data and at using DBI with text files
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Although they are the most basic of the database systems, text databases provide a reliable and safe location for storing information Many log systems using either delimited or fixed-length records and many of the files that you take for granted on Unix and Windows systems are actually text based, and are only imported or reported on when required If you look at a typical /etc/passwd file, you will notice that it has records one per line where the individual fields are separated by colons:
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root:x:0:1:0000-Admin(0000):/:/sbin/sh daemon:x:1:1:0000-Admin(0000):/: bin:x:2:2:0000-Admin(0000):/usr/bin: sys:x:3:3:0000-Admin(0000):/: adm:x:4:4:0000-Admin(0000):/var/adm: lp:x:71:8:0000-lp(0000):/usr/spool/lp: smtp:x:0:0:mail daemon user:/: uucp:x:5:5:0000-uucp(0000):/usr/lib/uucp: nuucp:x:9:9:0000-uucp(0000):/var/spool/uucppublic:/usr/lib/uucp/uucico listen:x:37:4:Network Admin:/usr/net/nls:
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There is a problem with the type of layout shown here if you start using this technique for more complex databases What happens if the data you are trying to store contains a colon As far as the Perl script is concerned, the colon specifies the end of one field and the beginning of the next An additional colon would only upset the information stored in the record Even worse, what would happen if you wanted to record multiple lines of text in the database Individual records are often stored on individual lines; multiline fields would confuse the script again You could use separate record delimiters that don t rely on the newline character, but again, this adds more complexity There are ways around these problems You could use a different character for the field and record separators, although this is still open to the same abuse and possible results You could just remove the field and record separator characters from the source before you put them in the database, but this reduces the utility of being able to store the information in the first place The simplest solution is to ignore any field or record separators and instead use fixed-length records to store the information The use of fixed-length records implies that you know the maximum size of the data that you are storing before you place it into the database, and therefore you need to know the format of the database before you write to and read from it Using fixed-length records would allow you to store any sort of information in the database, including multiple-line text, without worrying about how the data may affect the database layout The only problem with fixed-length databases is that you not only restrict the amount of information you can store, but you also increase the size of the data file for small records, as the individual fields are padded to make up the fixed lengths To complicate matters further, you may have trouble choosing a padding character that won t affect the contents of the fields you are storing Null characters, for example, produce all sorts of results when they are included as the text within a browser window when writing CGI programs In these situations, you can usually augment the fixed-length structure by also specifying the field length for each field in each record But this too increases the size of the database To add more complexity, you will also need to overcome the problems of searching the file if you are using it as a random-access database If you know the record number you want to access, then with either form of text database, you should be able to move to the location relatively quickly But if you don t know the record number, the time taken to find the data will be a factor of the database size This is why, practically, text databases are only good for small-scale installations or in situations where the information flow is basically one way Using a text database for storing log information is an example of a one-way information flow One or more programs will add data to the file without referring back to the data they have written Another script will be responsible for taking in the
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