re = /.*\b(PAL)\s?(\d+)\b.*/m
str = 'TCNU1573105 HDPE HTA108 155 155 000893520918 PAL990 25.2750 MT 28.9750 MT
TCNU1573105 HDPE HTA108 155 155 000893520918 PAL 990 25.2750 MT 28.9750 MT'
subst = '$1$2'
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