The following will come in handy for you in the regex:

\d - a digit
\w - a word character
\s - whitespace.
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This will allow you to put together things such as:

foreach my $line ( @lines ) {

  next unless $line =~ m/^\d{6} \w{3}/;
  # Will match '111111 aaa' where 1 is any
  # number, a any char.

  next unless $line =~ m/^\d+\s+\w+/;
  # Will match any number followed by any word.

  # The '^' anchors the search to the beginning
  # of the string.
}
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