Subject: Re: [Boston.pm] s/// with side effects?
SR> print "\t<" . ("tri state airport" =~ m//) . ">\n";
SR> $line =~ s/\r//gs;
SR> print "\t<" . ("tri state airport" =~ m//) . ">\n";
uri> you have run into a very obscure and now deprecated and soon to
uri> be replaced corner of perl. the empty regex actually doesn't
uri> match the empty string in m// (it does in split //!).
Obscure indeed. It's taken me many years to stumble over this one :)
uri> from perldoc perlop:
uri>
uri> If the PATTERN evaluates to the empty string, the last
uri> successfully matched regular expression is used instead.
kag> m// only sometimes means "match the empty pattern". Depending on
kag> context, it can also mean "match the same pattern again".
kag> The first m// has no previous pattern to reuse, so works as
kag> "match the empty pattern". The second does have a previous
kag> pattern, from the substitution, so works as m/\r/. "tri state
kag> airport" lacks carriage returns, so doesn't match.
Ken and Uri - thanks. That explains things perfectly.
Steve
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