1. There is no such thing as justification in plain text.
2. Using RTF (rich text) you might get the results you need. You might just find a standard 80 col width text file is easier to write to and create functions to align the text but if you want to use RTF then the syntax would be:
\ql Left-aligned (the default).
More information about rtf can be found here.
Note this is Microsoft RTF 1.6 and you might want to look into a more platform independent version of this solution.