You can do

$mod = 'My::Module1';
eval "use $mod";
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which is the same as

$mod = 'My::Module1';
($mod_file = $mod) =~ s{::}{/}g;
$mod_file .= '.pm';
require $mod_file;
$mod->import if $mod->can('import');
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The first two snippet imports the symbols if the module uses Exporter or similar. However, instead of importing, it be safer to do

$mod = 'My::Module1';
eval "require $mod";

$mod->function();
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The last snippet requires that function accept an extra initial argument.