(1)直接执行pkg_info命令可以查询目前系统已经安装的软件包：
[[email protected] ~]# pkg_info
(2)查询某个关键字相关的软件包有没有安装：
[[email protected] ~]#pkg_info | grep mail
cclient-2007e,1 Mark Crispin's C-client mail access routines courier-imap-4.8.0,2 IMAP (and POP3) server that provides access to Maildir mail dcc-dccd-1.3.116 Distributed Checksum Clearinghouse bulk email detector maildrop-2.5.0 Mail delivery agent (MDA) with filtering abilities mailgraph-1.14_3 A RRDtool frontend for Postfix statistics p5-Mail-DKIM-0.38 Perl5 module to process and/or create DKIM email p5-Mail-SpamAssassin-3.3.1 A highly efficient mail filter for identifying spam p5-Mail-Tools-2.06 Perl5 modules for dealing with Internet e-mail messages postfix-2.7.1,1 A secure alternative to widely-used Sendmail squirrelmail-1.4.20_2 A webmail system which accesses mail over IMAP
(3)查询某个文件属于那个软件包：
[[email protected] ~]# whereis postfix
postfix: /usr/local/sbin/postfix
[[email protected] ~]# pkg_info -W /usr/local/sbin/postfix
/usr/local/sbin/postfix was installed by package postfix-2.4.6,1
注：如果执行pkg_info -W file后没有显示任何信息，说明这个文件是freebsd系统内建的。
如执行pkg_info -W /bin/ls后是不会显示出任何信息的，说明ls文件是系统内建的！
(4)查询某个已安装的软件包含了有那些文件，所有pkg_add或ports方式安装的软件信息都在/var/db/pkg目录：
如要查找已安装的软件postfix包含有那些文件，可执行：
[root@www.sitkylin.com ~]# pkg_info |grep postfix
postfix-2.7.1,1 A secure alternative to widely-used Sendmail
根据已上显示的软件版本信息，继续执行以下命令即可：
[[email protected] ~]# pkg_info -L /var/db/pkg/postfix-2.7.1,1 |more