Maybe something like that?

$_ =  "foo        bar        baz     ";
my $catdesc = " extra ";

print join(",", ("", map /^\s*(.*\S)/, unpack("a10 a10 a10", $_), $cat
+desc)[0,0,-1,0,0,3,0,0,1,2,0] );

# output: ",,extra,,,baz,,,foo,bar,"
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(I simplified the format, because you didn't provide sample input, and I was too lazy to create a matching string)

That said, writing unnecessarily compact code usually isn't the best idea...

Update: added $catdesc to show that extra variables could in principle also be handled.