re = /(?:(?!AN-\d+).)+|(AN-\d+)/
str = '2 BILLING ID AN-19 RPS Ex : “00411850177 “
3 FILLER AN-11 RPS EX: “ “
4 FILLER AN-15 RPS EX: “ “
5 FILLER AN-30 RPS EX: “ “
6 FILLER AN-2 RPS EX: “ “
7 FILLER AN-1 RPS EX: “ “
8 BILLER CODE AN-4 RPS Ex : “1310” 1302 means PDAM Mitracom
9 FILLER AN-11 RPS EX: “ “
10 ADMIN FEE N-12 LPZ Ex : “000000075000” 11 FILLER AN-11 RPS EX: “ “
12 FILLER AN-12 RPS EX: “ “ '
subst = '$1'
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