@lines = (
           q{23.40:hello:this:is:a:line},
           q{123.38:this:is:another:line},
           q{7.32895:yet:another:line},
         );

@sorted = map { $_->[1] }
              sort { $a->[0] <=> $b->[0] }
                   map { [ (split(/:/,$_))[0], $_ ] }@lines;
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Of course, if you're going to split things anyhow, it might make just as much sense to go ahead and split the whole line and just use that.

@split = sort { $a->[0] <=> $b->[0] } map { [ split /:/ ] } @lines;
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