# How to renew command to add line after every section?

I am trying to add line after every section, at present I am adding it after every section, how do I add this once so that I don't have to explicitly add it every time. The code I used is:

\section*{$21^{st}$ March 2015}
\vspace{-0.6cm}
\noindent\textcolor{red}{\rule{\textwidth}{1mm}} \\ \\


Such changes are best done with the titlesec package. With a standard documentclass you can write:

\titleformat{\section}{\normalfont\Large\bfseries}{\thesection}{1em}{}[{\color{red}\titlerule[1mm]}]


since according the documentation of titlesec

\titleformat{\section}{\normalfont\Large\bfseries}{\thesection}{1em}{}


provides the standard section title format, and we just add the rule in the final optional argument for material after the title.

\documentclass{article}

\usepackage{color,titlesec}

\titleformat{\section}{\normalfont\Large\bfseries}{\thesection}{1em}{}[{\color{red}\titlerule[1mm]}]

\begin{document}

\section*{21\textsuperscript{st} March 2015}

\end{document}