When a module is installed in Perl, such as Net::SSH::Perl or Net::LDAP, the module adds information to a file called perllocal.pod on your system. The perllocal.pod is usually located at /usr/local/lib/perl5/version/arch/. The vast majority of modules appened information to the perllocal.pod file. The perldoc -l module_name command will determine if the perllocal.pod file contains an entry for a certain module. In this example, the Net::SSH::Perl module is installed on the system. Be care, as this search is CaSe SenSiTiVe.
~]# perldoc -l Net::SSH::Perl /usr/local/lib64/perl5/Net/SSH/Perl.pm
In this example, the Net::LDAP module is probably not installed, as there are not matches for Net::LDAP in the perllocal.pod file.
!]# perldoc -l Net::LDAP No documentation found for "Net::LDAP".