$message =~ s#(?<=\s)(http://\S+)#$1#g; ##

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$message =~ s#^(http://\S+)#$1#;
$message =~ s#(?<=\s)(http://\S+)#$1#g;

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$message =~ s#^(http://\S+[a-z])#$1#;
$message =~ s#(?<=\s)(http://\S+[a-z])#$1#g;

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use Regexp::Common qw( URI );
$message =~ s#^($RE{URI}{HTTP})#$1#;
$message =~ s#(?<=\s)($RE{URI}{HTTP})#$1#g;