perl6 -e  'say Date.new("2019-01-20"); say Date.new("2019-01"); '
2019-01-20
Invalid Date string '2019-01'; use yyyy-mm-dd instead
  in block <unit> at -e line 1

##</code><code>##


use Time::Piece; localtime()->strptime(@ARGV[0], "%Y-%m");


##</code><code>##


bash$    perl -e 'use Time::Piece; localtime()->strptime(@ARGV[0], "%Y-%m"); print "ok\n"; '  "2019-01"
ok


bash$    perl -e 'use Time::Piece; localtime()->strptime(@ARGV[0], "%Y-%m"); print "ok\n"; '  "2019-77"
Error parsing time at /usr/lib/x86_64-linux-gnu/perl/5.26/Time/Piece.pm line 481.