You're talking about undefined $/. Reading a whole file at once is called "slurping the file" or "slurping the file's content". 

my $file; { local $/; $file = <>; }
$file =~ s/(?<!\n)\n(?!\n)//g
print $file;

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Usage for above: 

perl script.pl infile > outfile

perl -i.bak script.pl file   # in-place

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As a one-liner: 

perl -0777pe's/(?<!\n)\n(?!\n)//g' infile > outfile

perl -i.bak -0777pe's/(?<!\n)\n(?!\n)//g' file

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In reply to Re: Can't remember the term to search for help on! by ikegami
in thread Can't remember the term to search for help on! by tom2112

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