convert bib file to \bibitem[\protect\citeauthoryear - latex

Question

I have a reference file (bib file) I want to convert it as
\bibitem[\protect\citeauthoryear{Allen C.W.}{1973}] {b1} Allen C.W., 1973,
Astrophysical quantities, ${3^{rd}}$ ed. (Athlone Press, London)
when I use
\nocite{*}
\bibliographystyle{apalike}
\bibliography{bibfile}
Output ppl file as
\bibitem[Allen, 1973]{allen1973astrophysical}
Allen, C.~W. (1973).

Answer 1

Combining natbib with the newapa style gives something similar:
\documentclass{article}
\usepackage{filecontents}
\begin{filecontents*}{\jobname.bib}
#BOOK{1973asqu.book.....A,
author = {{Allen}, C.~W.},
title = "{Astrophysical quantities}",
keywords = {ASTROPHYSICS, ASTRONOMICAL CONSTANTS, TABLES, HANDBOOKS},
booktitle = {London: University of London, Athlone Press, |c1973, 3rd ed.},
year = 1973,
adsurl = {https://ui.adsabs.harvard.edu/abs/1973asqu.book.....A},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
\end{filecontents*}
\usepackage{natbib}
\begin{document}
\cite{1973asqu.book.....A}
\bibliographystyle{newapa}
\bibliography{\jobname}
\end{document}
Resulting .bbl file:
\begin{thebibliography}{}
\bibitem[\protect\citeauthoryear{{Allen}}{{Allen}}{1973}]{1973asqu.book.....A}
{Allen}, C.~W. (1973).
\newblock {\em {Astrophysical quantities}}.
\end{thebibliography}