Two common patterns:

my ($substr) = $var =~ /(pattern)/;
print $substr, "\n"
   if defined $substr;
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if ($var =~ /(pattern)/) {
   print "$1\n";
}
[download]

Don't forget to put the parens around what you want to capture.

Update: Two common patterns for multiple matches:

my @substrs = $var =~ /(pattern)/g;
print "$_\n"
   foreach @substrs;
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while ($var =~ /(pattern)/g) {
   print "$1\n";
}
[download]