This is MetaPost, version 1.999 (TeX Live 2015/Debian) (kpathsea version 6.2.1)  7 SEP 2018 12:59
**./line.mp
(/usr/share/texlive/texmf-dist/metapost/base/mpost.mp
(/usr/share/texlive/texmf-dist/metapost/base/plain.mp
Preloading the plain mem file, version 1.005) ) (././line.mp
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1 output file written: line.ps