> $^N

indeed

use v5.12;
use warnings;

my $str ='43:1:1; 43:1:2; 43:1:3; 43:1:4; 43:1:5; 43:1:6; 27:3:7; 27:3
+:8; 27:3:9; 65:1:4; 65:1:18';
say $str;

$str =~ s#(\d+:\d+:)(\d);(?: \1((??{$^N+1}));)+#$1$2-$3#g;
say $str;

[download]

C:/Strawberry/perl/bin\perl.exe -w d:/tmp/pm/sequencer.pl 
43:1:1; 43:1:2; 43:1:3; 43:1:4; 43:1:5; 43:1:6; 27:3:7; 27:3:8; 27:3:9
+; 65:1:4; 65:1:18
43:1:1-6 27:3:7-9 65:1:4; 65:1:18

Compilation finished at Wed May 26 15:46:31

[download]

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery

PS: beautifying with /x modifier and adding missing ; in replacement left for the interested reader. :)

In reply to Re^2: Regexp substitution on variable-length ranges with embedded code? ( $^N ) by LanX
in thread Regexp substitution on variable-length ranges with embedded code? by Polyglot

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