>perl -wMstrict -le
"my $s = ',42 MAN:113 some other test 666.... MAN 231,456 TEXT'
       . 'text alpha Man 999 etc..77789 etc man 111,222,333'
       ;
 print qq{[[$s]]};
 ;;
 my $man = qr{ (?i) man :? }xms;
 ;;
 my @n = $s =~ m{ (?: \G (?<! \A) \s* , | $man) \s* (\d+) }xmsg;
 printf qq{'$_' } for @n;
"
[[,42 MAN:113 some other test 666.... MAN 231,456 TEXTtext alpha Man 9
+99 etc..77789 etc man 111,222,333]]
'113' '231' '456' '999' '111' '222' '333'
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See perlre and the sub-section '\G assertion' in the Regexp Quote Like Operators section (and, in general, the whole Regexp Quote Like Operators section) in perlop.