According to a web site I found:
148138 = 1988-5-16
148139 = 5/17/1988
these are two examples of lilian dates from an IBM website.
Using ksh,
function lil { datecalc -j $(( $1 - 100841)) ; }
defines a function and then "lil 148138" results in "1988 5 16". This function depends on my datecalc script.
And you know where to get datecalc, since it is mentioned in the "Yesterdays Date/Date Arithmetic" article in our FAQ section which you certainly read before you posted your question.
This was an interesting question. I had never heard of lilian date format before. It looks like IBM went to a lot of trouble to re-invent the wheel. As far as I can see, the only difference between lilian date format and the standard mjd is, well, 100,841 days.