You may need nested grouping toward the content based on the end of the spec, but at least the early part of a METAR should give you no concern.

The following approach embodies the advice (brilliant minds come to similar solutions?) re breaking the METAR or SPECI down into tokens:

#!/usr/bin/perl -lw
use strict;

my $metar = 'METAR CCCC 210855Z AUTO dddff(f)Gfmfm(fm)KTv dndndnVdxdxd
+x VVVVVSM [RDRDR/VRVRVRVRFT ] w\'w\' [NsNsNshshshs or VVhshshs T\'T\'
+/T\'dT\'d APHPHPHPH';

if ( $metar =~ /^(METAR|SPECI)\s([A-Z]{4})\s(\d\d)(\d{4}Z)\s(AUTO|COR)
+.*/) {
    my $type= $1; my $stn= $2; my $monthday = $3; my $obsTime= $4; my 
+$subtype= $5;
    print $type . " Station: $stn, Date: $monthday, ObservationTime: $
+obsTime, Subtype: $subtype";
} else {
print "ww screwed up the regex.";
}

[download]
($metar is taken straight from the ref doc, with digits substituted for YYGGgg and with the ticks escaped, as comprehensively understanding the spec would require more time than I have to give, just now.)

In reply to Re: Speeding up a large regex match pattern by ww
in thread Speeding up a large regex match pattern by wossname

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