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Advance Topics

Advance Topics. Topics. Packages Launching Programs Sockets Using Unix DBM. 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.

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Advance Topics

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  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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