x <- "% latex table generated in R 2.15.1 by xtable 1.7-0 package\n% Thu Jul 26 17:49:09 2012\n\\begin{table}[ht]\n\\begin{center}\n\\begin{tabular}{rlllr}\n  \\hline\ngrade & sex & disadvg & ethnicty & tlimth \\\\ \n  \\hline\n  6 & M & YES & HISPANIC &  43 \\\\ \n    7 & M & NO & BLACK &  88 \\\\ \n    5 & F & YES & HISPANIC &  34 \\\\ \n    3 & M & YES & HISPANIC &  65 \\\\ \n    8 & M & YES & WHITE &  75 \\\\ \n   \\hline\n\\end{tabular}\n\\end{center}\n\\end{table}\n"

cat(gsub("(?m)^(?:[^&]*&){1}\\s*([^&]*?)\\s*(?:&|\\\\)", "\\1XoX", x, perl = TRUE))