Iterators are important in the RPM2 package because they provide a more efficient interface to potentially large sets of packages, and because iterators more closely match the underlying C API. Furthermore, iterators are very easy to use. Simply call the next subroutine to move ahead to the next element, that is, the next package.

For example:

my $pkg_iter = $rpm_db->find_by_name_iter( "kernel" );

while (my $pkg = $pkg_iter->next() ) {

# Do something ...

}

Listing 18-3 shows a script that acts much like the rpm –q command, without any other command-line options.

Listing 18-3: rpmname.pl

#!/usr/bin/perl

#

# Queries RPM database for given package.

# Usage:

# rpmname.pl package_name

#

use strict;

use RPM2;

my $rpm_db = RPM2->open_rpm_db( "−path" => "/var/lib/rpm" );

my $pkg_iter = $rpm_db->find_by_name_iter( $ARGV[0] );

while (my $pkg = $pkg_iter->next() ) {

print $pkg->tag("NAME"), "-", $pkg->tag("VERSION"), "\n";

}

$rpm_db->close_rpm_db();

When you run this script, you need to pass the name of a package to query. For example:

$ ./rpmname.pl kernel

kernel-2.4.18