use strict;
my $str = '
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-mac"><code>R-SIG-Mac</code></a>: R Special Interest Group on Mac ports of R</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-db"><code>R-SIG-DB</code></a>: R SIG on Database Interfaces</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-debian"><code>R-SIG-Debian</code></a>: R Special Interest Group for Debian ports of R</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-dynamic-models"><code>R-SIG-dynamic-models</code></a>: Special Interest Group for Dynamic Simulation Models in R</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-ecology"><code>R-SIG-ecology</code></a>: Using R in ecological data analysis</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-epi"><code>R-SIG-Epi</code></a>: R for epidemiological data analysis</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-fedora"><code>R-SIG-Fedora</code></a>: R Special Interest Group for Fedora and Redhat ports of R</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-finance"><code>R-SIG-Finance</code></a>: Special Interest Group for ‘R in Finance’</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-geo"><code>R-SIG-Geo</code></a>: R Special Interest Group on using Geographical data and Mapping</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-gr"><code>R-SIG-gR</code></a>: R SIG on gRaphical models</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-gui"><code>R-SIG-GUI</code></a>: R Special Interest Group on GUI Development</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-hpc"><code>R-SIG-HPC</code></a>: R SIG on High-Performance Computing</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-insurance"><code>R-SIG-Insurance</code></a>: Special Interest Group on using R in actuarial science and insurance</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-jobs"><code>R-SIG-Jobs</code></a>: R SIG List for Announcements of Jobs where R is used</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-mediawiki"><code>R-SIG-mediawiki</code></a>: R SIG on the R Extension for Mediawiki</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-mixed-models"><code>R-SIG-mixed-models</code></a>: R SIG on Mixed Effect Models, notably lmer() related</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-networks"><code>R-SIG-networks</code></a>: R SIG for users and developers of network- or graph-related software within R</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-phylo"><code>R-SIG-phylo</code></a>: R SIG on phylogenetic and comparative methods and analyses</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-qa"><code>R-SIG-QA</code></a>: R SIG on Quality Assurance & Validation</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-robust"><code>R-SIG-Robust</code></a>: R SIG on Robust Statistics</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-teaching"><code>R-SIG-teaching</code></a>: SIG on Teaching Statistics (and more) using R</p></li>
<li><p><a href="https://stat.ethz.ch/mailman/listinfo/r-sig-wiki"><code>R-SIG-Wiki</code></a>: SIG on the Development of an “R Wiki”</p></li>
</ul>';
my $regex = qr/(<li><p><a href="https:\/\/stat.ethz.ch\/(m.*r-sig-)(.*)">.*)/p;
my $subst = '';
my $result = $str =~ s/$regex/$subst/rg;
print "The result of the substitution is' $result\n";
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html