This seems to work. 

sed 'N;s/\n/ /' list.txt

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To make it portable, you may need to replace ; with a newline, and possibly \n with some more portable thing to match a newline.

Update: indeed, this is a wrong solution. I didn't read the OP carefully. Sorry.

Update: \n is said to be portable.

In reply to Re: help writing simple perl script by ambrus
in thread help writing simple perl script by ashylarry

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