Don't work \immediate\write

Question

I'm writing my own .sty file. It contains its own table of contents and commands like \section{}, but nothing works because the output to the file for the table of contents does not work correctly

Here's what the output should look like:

\hyperref[mysection1]{\bfseries  3\hskip 1em\relax Section\dotfill  \pageref  {mysection1}}
\hyperref[mysection2]{\bfseries  3\hskip 1em\relax Section\dotfill  \pageref  {mysection2}}

аnd here's what it looks like:

\hyperref  [mysection3]{\bfseries  3\hskip 1em\relax Section\dotfill  \pageref  {mysection3}}
\hyperref  [mysection3]{\bfseries  3\hskip 1em\relax Section\dotfill  \pageref  {mysection3}}

Here is the code from .tex file:

\documentclass[10pt]{article}
\usepackage{cmap}
\usepackage[T2A]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[english,russian]{babel}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{setspace}
\usepackage{hyperref}
\usepackage{mysty}
\begin{document}
    \mytableofcontents
\section{Section}

\section{Section}

\end{document}

Here is the code from mysty.sty file:

\RequirePackage{amsmath}
\RequirePackage{amssymb}
\RequirePackage{setspace}
\RequirePackage{hyperref}
\newwrite\myoutput
\immediate\openout\myoutput=toc.tex
\newcounter{sections}
\setcounter{sections}{1}
\renewcommand{\section}[1]{%
\vspace{2ex}
\label{mysection\the\value{sections}}%
\noindent\textbf{\arabic{sections}.\quad #1}%
\write\myoutput{\hyperref[mysection\the\value{sections}]{\bfseries\the\value{sections}\quad #1\dotfill\pageref{mysection\arabic{sections}}}}%
\stepcounter{sections}

\vspace{2ex}

}
\newcommand{\mytableofcontents}{%
    \newpage\thispagestyle{empty}
    \noindent\textbf{Table of Contents}
\input{toc}

\newpage

}
\endinput

Answer 1

You missed \immediate before \write. The you can't be surprised that you have delayed \write.

Adding \immediate before \write without another changes yields to error, because the parameter of \write is immediately expanded. You want to expand only \the\value{sections}, nothing more.

Your line with \write in your mysty.sty should be:

    \immediate\write\myoutput
       {\string\hyperref[mysection\the\value{sections}]{\noexpand\bfseries\the\value{sections}\quad #1\string\dotfill\string\pageref{mysection\the\value{sections}}}}%

Answer 2

It's hard to understand why you want to do manually what the LaTeX kernel does better by itself.

Anyway, doing \immediate\openout\myoutput in the .sty file has the consequence that the toc file is cleared as soon as the file is loaded, so you will get nothing in the table of contents.

You must start writing it after the table of contents (as built in the previous run) has been typeset.

You also get no anchor if you do \stepcounter{sections}. You need \refstepcounter{sections} before \label (and to not initialize the counter to 1, of course).

Another obvious weakness of the code is that you're forced to have the table of contents at the beginning. With the standard \tableofcontents you can put it anywhere.

You also need to protect commands from expansion inside \write.

Here's a working version of your code. But you should not do it yourself: use the standard tools and customize them. For instance, as noted by David Carlisle, you may well get a section title at the bottom of a page, with the text in the following page.

Check for the differences.

\documentclass[10pt]{article}
\usepackage{cmap}
\usepackage[T2A]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[english,russian]{babel}
%\usepackage{mysty}
\makeatletter
\RequirePackage{amsmath}
\RequirePackage{amssymb}
\RequirePackage{setspace}
\RequirePackage{hyperref}
\newwrite\myoutput
\AtEndDocument{\immediate\closeout\myoutput}
\newcounter{sections}
\renewcommand{\section}[1]{%
    \par\vspace{2ex}
    \refstepcounter{sections}\label{mysection\the\value{sections}}%
    \noindent\textbf{\arabic{sections}.\quad #1}%
    \immediate\write\myoutput{%
      \noindent
      \noexpand\hyperref[mysection\the\value{sections}]{%
        \noexpand\bfseries\the\value{sections}\noexpand\quad #1%
        \noexpand\dotfill\noexpand\pageref{mysection\arabic{sections}}%
      }%
      \noexpand\par
    }%
    \par\vspace{2ex}
}
\newcommand{\mytableofcontents}{%
    \newpage\thispagestyle{empty}
    \noindent\textbf{Table of Contents}\par
    \InputIfFileExists{\jobname.toc}{}%
    \newpage
    \immediate\openout\myoutput=\jobname.toc
}
\makeatother
\begin{document}
\mytableofcontents
\section{Section}
\section{Section}
\end{document}