re = /^\d{4}\s+\d{2}([A-Z ]*?[A-Z])\s*\d.*/m
str = '0010 00LTT BOX PCS RH039349 0101113140 DE1 D 1
1210 02EXH BX PCS RH 060644 010111 DL5 D 1
0010 00PLATE BENT 039348 0101116201 DE1 B 1
0010 00PLATE BENT RH 039348 0101116201 DE1 C 1
0010 00ANGLE 038310 0101110200 DD1 B 1'
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