How to insert a running heads after Opening Page?

Question

After Opening Page running heads should always be [running authors], no matter what's the page number (Odd/Even). Then the next page should be [short Title].

Opening Page - Empty
Second Page - [running authors] (Odd/Even Pages)
Third Page - [Short Title] (Odd/Even Pages)
4th Page - [running authors] (Odd/Even Pages)
5th Page - [Short Title] (Odd/Even Pages)

so on....

Answer 1

If you want the same running head for each page, the code is pretty simple.

It's enough to write into your preamble:

\renewcommand\rightmark{[Short Title]}
\renewcommand\leftmark{[running authors]}

Where \leftmark and \rightmark are the contents of respectively left page head and right page head. So you could write a document like:

\documentclass[openany]{book}

\renewcommand\rightmark{[Short Title]}
\renewcommand\leftmark{[running authors]}

\begin{document}

\part{Introduction}
    \chapter{Bla} \newpage Bla\newpage Bla 
    \newpage Bla\newpage Bla \newpage Bla\newpage Bla 

\part{Example 1:\\Foo}
    \chapter{Bla} \newpage Bla\newpage Bla 

\part{Appendix}
    Bla \newpage Bla\newpage Bla 

\end{document}

and have correct running heads as desired. I prefer this rather than using fancyhdr.

Answer 2

There's little need to tap into the \author and/or \title macros to extract what you need. It's probably just as easy to retype the authors and short title in a fancyhdr implementation.

If you're using a twoside setup, then fancyhdr allows for specifying a Even/Odd header:

\documentclass[twoside]{article}
\usepackage{fancyhdr,lipsum}
\pagestyle{fancy}
\fancyhf{}% Clear header/footer
\fancyhead[CE]{[running authors]}% Centred header on Even page
\fancyhead[CO]{[Short title]}% Centred header on Odd page
\begin{document}
\thispagestyle{plain}
\lipsum[1-20]

\end{document}

Setting \thispagestyle{plain} ensures that the first page has the default plain page style. The above also assumes that you're using a twoside article display.

If you're not using a twoside article, then you could condition on whether or not \value{page} is odd/even - inside the header/footer this is fine, as page styles are set appropriately during shipout; one reason why \thepage works in these areas.

\documentclass{article}
\usepackage{fancyhdr,lipsum}
\pagestyle{fancy}
\fancyhf{}% Clear header/footer
\fancyhead[C]{%
  \ifodd\value{page}\relax
    [Short title]% Odd page header
  \else
    [running authors]% Even page header
  \fi}
\begin{document}
\thispagestyle{plain}
\lipsum[1-20]

\end{document}

Fundamentally, both approaches above assume that the opening page is numbered 1 (odd), making the second page even, and so forth.