re = /(\d\d\d\d)-(\d\d)(-\d\d\D)?/
str = 'ABC 2012-10-01
DEF 2013-07-10
2018-01-21
ABG 2015-10-30A
EDF 2019-01-19B
ABC/DEF/GEH 2019-01-19A
'
subst = ''
result = str.gsub(re, subst)
# Print the result of the substitution
puts result
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Ruby, please visit: http://ruby-doc.org/core-2.2.0/Regexp.html