I assume you meant

@arr = qw(test1 @test2 @test3 test4 test5);
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In that case, you can use grep

$str1 = join(',', grep {/^@/} @arr);
$str2 = join(',', grep {/^[^@]/} @arr);
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Or you could use a foreach loop, push onto either of two arrays depending on the match, then join afterward.