9 1 DBM Databases CGI/Perl Programming By Diane Zak.
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Transcript of 9 1 DBM Databases CGI/Perl Programming By Diane Zak.
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DBM Databases
CGI/Perl Programming
By Diane Zak
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Objectives
• In this chapter, you will:
• Create and open a DBM database• Add a record to a DBM database• Modify and delete a record in a DBM
database• Determine whether a DBM database
contains a specific key
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Objectives
• In this chapter, you will:
• Close a DBM database• Concatenate strings• Create a “here” document
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Introduction• Most businesses store information in
databases:– Inventory– Employee information– Customer information
• Databases can be created with a database software package:– Oracle– Microsoft Access– Sybase– MySQL
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Introduction• The Perl DBI module is used with the
appropriate DBD file to manipulate the database– DBI = Database Interface– DBD = Database Driver
• One of the Perl DBM modules can also be used to create and manipulate a DBM database– DBM = Database Management
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The Jeffrey Sikes Band Form
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Planning and Coding the Jeffrey Sikes Band Script
– is used to display a blank space in a Web page
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Creating and Openinga DBM Database
• Examples of Perl DBM modules:– ODBM_File.pm– NBDM_File.pm– SDBM_File.pm
• Will concentrate on SDBM because it is included in the standard Perl distribution for Windows and UNIX
• To use the module, need to include the line:
– use SDBM_File;
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Creating and Openinga DBM Database
• Good programming practice to plan a database before creating it– List the fields to include in each record– Identify the primary key in the list
• A unique identifier of a record• In this mailing list database – email address• A primary key can be more than one field
• DBM modules store records on disk using a key/value format – like a hash– key – data entered in each record’s primary key field– value – data entered in the remaining fields in the
record
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Creating and Openinga DBM Database
• The tie function is used to create and open a DBM database on disk– The die function
can be used to display a message and exit a script if the tie function fails
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Creating and Openinga DBM Database
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Adding and Modifying a Record in a DBM Database• A record is added to a DBM database by
adding a key/value pair to the hash tied to the database
• A record is modified by modifying the value corresponding to an existing key in the database
• Must make changes only through the tied hash– Cannot make changes directly to the DBM
database
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Adding and Modifying a Record in a DBM Database
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Closing a DBM Database
• Use the untie function to close a DBM database– Remove the tie that binds the
database to the hash– Syntax:
• untie (hash)
– Example:• untie (%mail)
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The Jeffrey Sikes Band Script – add function
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Determining if a Specific Key is in a DBM Database
• The exists function can be used to determine if a specific key is contained in a DBM database– Syntax:
• exists ($hash {key})
– Example:• if (exists ($mail {$email}))
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Deleting a Record From a DBM Database
• The delete function is used to delete a record from a DBM database– Syntax:
• delete ($hash {key})
– Example:• delete ($mail {$email})
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Concatenating Strings
• The concatenation operator (.) is used to connect multiple strings
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The Jeffrey Sikes Band Script – remove function
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Completed band.cgi Script
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Creating a “here” Document
• Most CGI scripts contain many print statements specifically to output HTML code
• A “here” document allows you to use one print statement for a block of HTML code
• Syntax:print <<label;HTML instructionslabel
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Creating a “here” Document• Example of a “here” document:
#create Web pageprint <<endHtml;<HTML><HEAD><TITLE>The Jeffrey Sikes
Band</TITLE></HEAD><BODY BGCOLOR=silver><FONT SIZE=5><H1>The Jeffrey Sikes Band</H1>Thank you, $name. We will send the monthly newsletter
to $email.</FONT></BODY></HTML>endHtml
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Creating a “here” Document
• If the label of a “here” document is multiple words, you need to put single or double quotation marks around label.– If label is enclosed in single quotation
marks, variable interpolation will not occur.
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Summary• A database is a collection of data that is stored in a disk
file and organized so that its contents can be easily accessed, managed, and updated.
• One of the Perl DBM (Database Management) modules can be used to create and manipulate a DBM database: – SDBM_File.pm, ODBM_File.pm, NDBM_File.pm.
• The data contained in a DBM database is stored on disk using a key/value format.
• The tie function can be used to create and open a DBM database.– Syntax: tie (hash, module, filename, flag, mode)
• flag – O_CREAT, O_RDONLY, O_WRONLY, O_RDWR are defined in the Fcntl module
• mode – 0666 if O_CREAT flag, otherwise 0
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Summary• The tie function can be used to create and open a DBM database.
– Syntax: tie (hash, module, filename, flag, mode)• flag – O_CREAT, O_RDONLY, O_WRONLY, O_RDWR are defined in the Fcntl
module• mode – 0666 if O_CREAT flag, otherwise 0
• The die function can be used to display a message and exit a script if tie function fails.
• To add or modify a record in a DBM database:– Syntax: $hash{key} = value;
• key – data in record’s primary key field• value = data contained in remaining fields in record
• The untie function can be used to close a DBM database.– Syntax: untie (hash)
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Summary
• The SDBM_File module creates 2 files for the database: filename.dir and filename.pag
• The exists function can be used to determine if a key is in a DBM database.– Syntax: exists ($hash {key})
• The delete function can be used to remove a record from a DBM database.– Syntax: delete ($hash {key})
• String concatenation operator is the period (.)
• A “here” document can be used to send HTML code to the browser
