Well, it looks like you are attempting to set autoflush in line 4 but you forgot the $ in front of the |. Or is that just a bad pasting job?

Also, regarding that big unless statement. Is that an attempt to get rid of the /bin/sh in the output? You would do better with a single regex. Something like:

unless $input=~m|^(?:/bin/sh|\$\s|/)|;
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Bye