I inserted an unlikely string next to the keywords and then used split.

my $input = "pro my project cOn my customer dAte 2009-10-5 at 17:00 pr
+i 2 msg Rack new server";
print "input=$input\n";

my @keywords = qw(pro con date at pri msg);
my $splitmarker = "___YABBA_DABBA_DOO___";
my %results;

$input =~ s/\b($_)\b/$splitmarker$1/i foreach @keywords;

my @parts = split /$splitmarker/,$input;
foreach (@parts)
{
    $results{lc($1)} = $2 if /(\w+)\s+(.+?)\s*$/;
}

foreach (@keywords)
{
    print "$_ = \"$results{$_}\"\n" if exists $results{$_};
}
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