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Advanced Programming with Perl: Packages, Socket Communication, and DBM Databases

This guide covers advanced topics in Perl programming, focusing on packages, socket communication, and Unix DBM (Database Management). Learn how to define and use packages to structure your code effectively while avoiding name conflicts. Discover socket communication techniques for inter-process communication, implementing client-server models. Additionally, delve into persistent storage using DBM databases, including how to create and manage key-value pairs efficiently. These concepts empower developers to build robust and streamlined applications.

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Advanced Programming with Perl: Packages, Socket Communication, and DBM Databases

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Presentation Transcript

  1. Advance Topics

  2. Topics • Packages • Launching Programs • Sockets • Using Unix DBM

  3. Packages • Every program has a main package. • A program can use other packages • use <name>; • The programmer can also define packages. • package <name>; • The rest of the file is the body of the package. • The name of the file is <name>.pm

  4. Packages (cont.) • Each package has its own namespace. • Reduces the risk of name conflicts. • Functions: <name>::<function name> • e.g. String::length • Global vars: <var symbol><name>::<var> • e.g. $String::foo • my can be used to prevent access: Package private; my $private_var;

  5. Launching Programs • Almost all programming languages allow their programs to call subprograms. • Perl is no exception. • Perl has several ways to launch a program. • Two most common are: • backquote (`) • system • Perl also includes fork and exec.

  6. backquote • Place the name of the subprogram in (`). • Synchronous execution. • Return value is the output of the subprogram. • For example, $date = `date`; print “$date \n”;

  7. system • Pass subprogram’s name to system. • Synchronous execution. • Return value is the execution status of the subprogram. • Subprograms output is directed to STDOUT. • For example: system(“date”);

  8. Socket Communication • Provides a powerful way to communicate between computers, programs, etc. • Based on the notion of clients and servers. • Usage is similar to files: • Programs read from and write to sockets. • Supported by Perl’s Socket module. • use Socket;

  9. A Client/Server Example

  10. Unix DBM • Unix has a simple DataBase Management (DBM) system. • A DBM database is a list of key/value pairs. • Structure similar to Perl’s hash. • DBM databases are connected to hash. • DBM provides persistent hashes.

  11. DBM (cont.) • A DBM database is stored in two files: • <name>.pag: Stores the data. • <name>.dir: Index into the .pag file. • dbmopen is used to create and open DBM databases. • dbmclose breaks connection between hash and database.

  12. dbmopen/dbmclose • dbmopen (<hash>, <dbname>, <mode>) • e.g. dbmopen (%salaries, salary_db, 0666); • e.g. dbmopen (%salaries, salary_db, undef); • dbmclose (<hash>) • e.g. dbmclose (%salaries);

  13. An Example dbmopen (%salaries, salary_db, 0666) || die “Could not open salary_db $!”; print “Enter an employee’s name: ”; while ($name = <STDIN>) { chomp $name; print “Enter the salary: ”; $salaries{$name} = <STDIN>; print “Enter an employee’s name: ”; } dbmclose (%salaries);

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