Place preamble packages in a different tex file

Question

I have the following main tex file and I wish to place the \usepackage commands in a different usepackage.tex file and compile it on main tex file. How can I do that. I tried but keep getting error as if it does not know where to find the file usepackages. (Pardon me for the messy packages, I know it is a disaster, I am trying to fix it now.)

\documentclass[12pt,a4paper,twoside]{report}
\setlength{\textwidth}{16cm}
\setlength{\oddsidemargin}{0pt}
\setlength{\evensidemargin}{0pt}
\setlength{\parskip}{3mm}
\setlength{\parindent}{0mm}
\usepackage[utf8]{inputenc}
\usepackage{graphicx}
\graphicspath{{images/}}
\usepackage{setspace}
%\usepackage{biblatex}
%\usepackage{url}
\usepackage{epsfig}
\usepackage{filecontents}
\usepackage{xparse,nameref}
%\usepackage{hyperref}
\usepackage{mathrsfs}
\usepackage[nokeyprefix]{refstyle}
\usepackage{mathtools}
\usepackage{thmtools}
\usepackage{enumerate}% http://ctan.org/pkg/enumerate
\usepackage{enumitem}
\usepackage{thm-restate}
\usepackage{cleveref}
\usepackage{amsmath}
\usepackage{url}
\usepackage{amsthm}
\DeclareMathOperator{\lcm}{lcm}
\DeclareMathOperator{\ord}{ord}
\usepackage{cellspace}
\setlength\cellspacetoplimit{4pt}
\setlength\cellspacebottomlimit{4pt}
\usepackage{booktabs}
\setlength\defaultaddspace{2ex}
\usepackage{graphicx}
\usepackage{array}
\usepackage{tabularx,ragged2e,booktabs,caption}
\usepackage[figuresleft]{rotating}
\usepackage{rotating}
\newcolumntype{C}{>{\Centering\arraybackslash}X}
\newcommand\swb{{\scriptstyle\Box}} % "small white box"
\usepackage{mathtools}
\usepackage{tikz}
\usetikzlibrary{positioning}
\usetikzlibrary{arrows}
\setcounter{secnumdepth}{3}
\usetikzlibrary{shapes.multipart}
\usepackage{tabu}
\usepackage{amssymb,bm}
\usepackage{framed}
\usepackage{upgreek} %use uptau greek letter
\usepackage{comment} %choose parts not to compile
\usepackage{tikz}
\tikzset{mynode/.style={fill=white,text=black,font=\tiny,inner sep=1pt}}
\usepackage[toc,page]{appendix}
\addtolength{\topmargin}{-.875in}
\newenvironment{numberlists}[1][3\parindent] %for long numberlist command
 {\begin{list}{}{%
   \leftmargin=#1\relax
   \rightmargin=\leftmargin
   \itemsep=\jot
   \parsep=0pt
   \partopsep=0pt
   \labelsep=0pt}}
 {\end{list}}
\newcommand\numlist[2]{%
  \item[]\makebox[0pt][r]{$#1=\lbrack$}%
  \begingroup
  \begingroup\lccode`~=`,\lowercase{\endgroup\def~}{\mathcomma\penalty0 }%
  \mathcode`,="8000
  \thinmuskip=6mu plus 6mu minus 2mu
  $#2\rbrack$%
  \endgroup
}
\mathchardef\mathcomma=\mathcode`, %end of numberlist command
\setlength{\oddsidemargin}{-1in}   \setlength{\evensidemargin}{-1in}
\addtolength{\oddsidemargin}{25mm}\addtolength{\evensidemargin}{20mm}
\setlength{\marginparwidth}{40pt} \setlength{\marginparsep}{10pt}
\setlength{\topmargin}{-5mm}      \setlength{\headsep}{0.5in}
\setlength{\textheight}{227mm}    \setlength{\textwidth}{165mm}
\renewcommand\floatpagefraction{0.8} %   Default = 0.5
\usepackage{listings}
\usepackage{color}
\definecolor{dkgreen}{rgb}{0,0.6,0}
\definecolor{gray}{rgb}{0.5,0.5,0.5}
\definecolor{mauve}{rgb}{0.58,0,0.82}
\lstset{
  language=Java,
  aboveskip=3mm,
  belowskip=3mm,
  showstringspaces=false,
  columns=flexible,
  basicstyle={\small\ttfamily},
  numbers=none,
  numberstyle=\tiny\color{gray},
  keywordstyle=\color{blue},
  commentstyle=\color{dkgreen},
  stringstyle=\color{mauve},
  breaklines=true,
  breakatwhitespace=true,
  tabsize=3
}

\allowdisplaybreaks % allow page breaks
\begin{document}
\begin{titlepage}
\begin{center}
\includegraphics[width=0.70\textwidth]{logo} \\[2cm]

{ \large \bfseries Perfect Triangles : Rational points on Elliptic Curves }\\
Shahrina Ismail \\
\{Candidate's academic degrees\} \\[7cm]
{\em A thesis submitted for the degree of Doctor of Philosophy at\\
The University of Queensland in 2016} \\
School of Mathematics and Physics

\end{center}
\end{titlepage}

\pagenumbering{roman}

\theoremstyle{definition}

\begin{abstract}
here...
\end{abstract}

\tableofcontents

\listoffigures

\listoftables

\newpage
\pagenumbering{arabic}
\onehalfspacing
\chapter{Introduction}
\input{chapters/Introduction}

\onehalfspacing
\chapter{Background and Methodology}\label{chap:2}
\input{chapters/chapter2}


\onehalfspacing
\chapter{Values of $\delta(\mu)$}\label{chap:3}
\input{chapters/chapter3}

\end{document}

Answer 1

I suggest you

• Place all preamble instructions -- other than the \documentclass instruction, of course -- in a separate file, to be called (say) sharina.sty. (Note the filename extension). Save the file in the directory where your main tex file is located.

• Place the single instruction

  \usepackage{sharina}
  

  in the preamble of your tex file. Observe: No filename extension.

  With this change, the document preamble should consist of only the following two lines:

  \documentclass[12pt,a4paper,twoside]{report}
  \usepackage{sharina}
  

Then, do please take the time to clean up and simplify the instructions contained in the file sharina.sty.