What input are you trying?

If indeed you've tried this string:

............ keyword=nn ............
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Then the regexp you've used won't work. It'll brake right after the 'keyword=' part as 'nn' string doesn't match '\d+' expression.

However, this works:

while(<DATA>) {
  m/^(.+?\s+keyword=)(\d+)(\s+.+)$/;
  print "$1-" if $1;
  print "$2-" if $2;
  print "$3" if $3;
  print "\n";
}

__DATA__
............ keyword=12 ............
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# Under Construction
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