in reply to Re: Match a pattern only if it is not within another pattern
in thread Match a pattern only if it is not within another pattern

sorry, this doesn't work... 
$str =~ s/((?<!bar)\S*)foo(\S*(?!qux))/${1}123${2}/gx;

print "$str\n";

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prints

bl123 and barthis123thatqux and barso123quxhim and123som 123

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