The standard place they(distros) put Perl is in /usr/bin/perl. When you are logged into Ubuntu, run this command

find `perl -e 'print "@INC"'` -name "*.pm"
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All you need to do to use use is USE itelf.

# for example
use CGI;
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You can specify any location you want, by putting this in your ubuntu .bashrc file

export PERL5LIB=$PERL5LIB:/home/myusername/perl5
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Many of the local homedir installers, will put it in /home/usr/perl5, so making a directory /home/yourusername/perl5 would be a good choice, and add it in your .bashrc file.