kenclark: Another approach to the problem is to say exactly what you want to do: trim all whitespace at the absolute beginning  \A or at the absolute end  \z of the string. This avoids any confusion with the various meanings of the  ^ $ metacharacters. With a PBP-style substitution regex: 

>perl -wMstrict -le
"my $para =
   qq{\n\n  \t  \nsentence 1\nsentence 2\n\nsentence    3\n\n  \t\n};
 print qq{[[$para]]};
 ;;
 $para =~ s{ \A \s+ | \s+ \z }{}xmsg;
 print qq{[[$para]]};
"
[[


sentence 1
sentence 2

sentence    3


]]
[[sentence 1
sentence 2

sentence    3]]

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In reply to Re^2: Trim blanks from the beginning and end of a multi-line string by AnomalousMonk
in thread Trim blanks from the beginning and end of a multi-line string by kenclark

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