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Join Lines 
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$ echo {1..10} | xargs -n 1 > InputFile.dat
$ sed -n 'H;${g;s/\n/ /gp;}' InputFile.dat

#join all non blank lines
$ sed -n 'H;/^ *$/{x;s/\n/ /gp;s/.*//;x;p;d;};${s/\n/ /gp;p;}' InputFile.dat