re = /^(?:.*?\bRationale-|Normal|List Paragraph\t(?:\d+\)[ \t]*)?)[ \t]*/m
str = 'List Paragraph 36) Rationale-1 - Details on the context:
List Paragraph 37) None.
Normal
List Paragraph 38) 2 - Statement complements:
List Paragraph 39) Blablablabla
List Paragraph (1) Blablablabla
List Paragraph (2) Blablablabla
List Paragraph (3) Blablablabla
List Paragraph (4) Blablablabla
List Paragraph (5) Blablablabla
List Paragraph (6) Blablablabla
List Paragraph (7) Blablablabla
Normal
List Paragraph 40) Blablablabla
Normal
List Paragraph 41) 3 - Statement justification:
List Paragraph 42) Blablablabla
Normal
List Paragraph 43) Blablablabla
List Paragraph 44) Blablablabla
List Paragraph 45) Blablablabla
List Paragraph 46) Attached Files: Rationale-
Normal'
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