\frametitle{Regex Flavors: A Shell Caveat}
\begin{block}{Comparison}
\begin{center}
\begin{tabular}{llll}
Feature & BRE (Basic) & ERE (Extended) & PCRE (Perl/JS/Py)\\
\hline
Tools & \texttt{grep}, \texttt{sed} & \texttt{grep -E}, \texttt{awk} & \texttt{grep -P}, Python\\
\texttt{+}, \texttt{?} & Need \texttt{\textbackslash{}} & Raw: \texttt{+}, \texttt{?} & Raw: \texttt{+}, \texttt{?}\\
\texttt{()}, \texttt{\{\}} & Need \texttt{\textbackslash{}} & Raw: \texttt{()}, \texttt{\{\}} & Raw: \texttt{()}, \texttt{\{\}}\\
\end{tabular}
\end{center}

\begin{itemize}[<+->]
\item \alert{Note:} macOS BSD \texttt{grep} usually lacks \texttt{-P}. Prefer \texttt{grep -E} or install GNU \texttt{grep} (often \texttt{ggrep}).
\end{itemize}
\end{block}
\begin{exampleblock}{Example: Matching "1 or more"}\label{sec:org189b4f5}
\begin{itemize}
\item \alert{BRE:} \texttt{grep 'a\textbackslash{}+'}
\item \alert{ERE:} \texttt{grep -E 'a+'}
\item \alert{PCRE:} \texttt{grep -P 'a+'}
\end{itemize}
\end{exampleblock}
