A few points about your code.

• In your pattern \d{1} is exactly the same as saying \d, IOW a quantifier of one is implicit and needn't be stated.

• Be aware that a full stop is a regular expression metacharacter matching any character (with caveats, see perlre) so did you mean to match a decimal point in this pattern /returns \d{1} \(in \d{1}.\d{6} secs/? Consider this code

  $ perl -le '
  > print
  >    m{\d{1}.\d{6}}
  >    ? qq{$_: Matched}
  >    : qq{$_: No match}
  >    for
  >       q{in 1.234567 secs},
  >       q{in 12345678 secs},
  >       q{in 3A987654 secs};'
  in 1.234567 secs: Matched
  in 12345678 secs: Matched
  in 3A987654 secs: Matched
  $
  [download]

  You will need to escape the dot if you want a decimal point

  $ perl -le '
  > print
  >    m{\d{1}\.\d{6}}
  >    ? qq{$_: Matched}
  >    : qq{$_: No match}
  >    for
  >       q{in 1.234567 secs},
  >       q{in 12345678 secs},
  >       q{in 3A987654 secs};'
  in 1.234567 secs: Matched
  in 12345678 secs: No match
  in 3A987654 secs: No match
  $
  [download]

  Now only a literal full-stop is matched.

• Consider using the three-argument form of open with lexical filehandles.

• Avoid using the variable names $a and $b as they are special and should be reserved for use in sort routines.

I hope these points are helpful.