단어의 첫 글자만 다르게

dofirst.tex

% see http://www.ktug.org/xe/index.php?document_srl=214192
\def\dofirst#1{\dodofirst#1 \stopdofirst{} }
\def\dodofirst#1 {%
  \ifx\stopdofirst#1%
    \unskip
  \else
    \in@{,#1,}{,a,am,an,of,for,in,on,the,to,with,}%
    \ifin@
    \else
      \expandafter\DoFirst
    \fi
    #1 %
    \expandafter\dodofirst
  \fi
}
\def\DoFirst#1{\uppercase{\textbf{#1}}}

\dofirst{I am happy to join with you today.}