If you want a one-liner, put it all on one line! 

perl -i.bak -e "local $/; $_=<>; 1 while s/^(([ ]+)(?![ ])[^\n]+)\n\2(
+?![ ])/$1/m; print" myfile.txt

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In reply to Re^3: replace \n with space to join indented lines by ikegami
in thread replace \n with space to join indented lines by olivier

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