Taking advantage of specific features of your regexp,

@matches = map { /^(\d\s+foo)/; $1 } /(?:\d\s+foo[^\r\n]*)/g;
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This will validate and return matches. If you just wish to validate, the following will suffice:

# Specific case:
/(?:\d\s+foo[^\r\n]*)/;

# General case:
$repeated = qr/\d\s+foo/;
/(?:$repeated[^\r\n]*)$repeated/;
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Update: My capture version has two issues. And the pattern is still repeated.

You really do want a parser for this:

list  : term list_  { [ $item[0], $item[1], @{$item[2]} ] }

list_ : sep term    { [ $item[1], @{$item[2]} ] }
      |             { [ ] }
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