With this preamble :

\documentclass[12pt,a4paper,twoside]{book}
\usepackage[top=2.5cm,bottom=2.5cm,right=2.5cm,left=2.5cm]{geometry}
\usepackage[T1]{fontenc}
\usepackage[latin1]{inputenc}
\usepackage{flshort}
\usepackage{shortvrb,latexsym}
\usepackage[french]{mylayout}
\usepackage{lettrine}
\usepackage{makeidx}
\usepackage[frenchb,english]{babel}
\usepackage{pb-diagram}
\usepackage{amsfonts}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amscd}
\usepackage{amsthm}
\usepackage{mathrsfs}
\usepackage{graphics}
\usepackage{graphicx}
\usepackage[all]{xy}
\usepackage{enumitem}
% Les ensembles math{\'e}matiques, utilisant l'extension amsfonts
\renewcommand{\footrulewidth}{1pt}
\def\N{{\mathbb{N}}}
\def\Z{{\mathbb{Z}}}
\def\Q{{\mathbb{Q}}}
\def\R{{\mathbb{R}}}
\def\C{{\mathbb{C}}}
\newtheorem{thm}{Th\'eor\eme}[section]
\newtheorem{lemma}{Lemma}[section]
\newtheorem{pro}{Proposition}[section]
\newtheorem{conj}{Conjecture}[section]
\newtheorem{cor}{Corollaire}[section]
\newtheorem{axiom}{Axiom}[section]
\theoremstyle{definition}
\newtheorem{dfn}{D\'efinition}[section]
\newtheorem{exs}{Exemples}[section]
\newtheorem{ex}{Exemple}[section]
\newtheorem*{rem}{Remarque}
\theoremstyle{remark}
\newtheorem*{note}{Note}
\newtheorem{cas}{Cas}
\newcommand{\p}{{\mathfrak{p}}}
\newcommand{\m}{{\mathfrak{m}}}
\renewcommand{\P}{{\mathbb{P}}}
\newcommand{\Rr}{\mathbb{R}}
\newcommand{\n}{{\mathfrak{n}}}
\renewcommand{\A}{{\mathbb{A}}}
\begin{document}
\selectlanguage{frenchb}
\tableofcontents
\end{document}


I get

I don't know how I can adjust the length of line in Header/Footer can someone help me to solve this problem?

Edit (flshort.sty)

     %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Contents: Special Commands for the LShort2e Introduction
% $Id: flshort.sty,v 1.7 2001/11/25 17:43:58 matthieu Exp$
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% By Tobias Oetiker
% Modified by Matthieu Herrb to handle the french extension
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%\errorcontextlines=10
%save pageref an label
\let\lsspageref=\pageref
\ProvidesPackage{flshort}
\RequirePackage{verbatim}
\RequirePackage{fancyhdr}
\RequirePackage{calc}
\RequirePackage{ifthen}
%
% Lets have some nice headings
%
\pagestyle{fancyplain}
\renewcommand{\chaptermark}[1]{\markboth{#1}{}}
\renewcommand{\sectionmark}[1]{\markright{\thesection{} #1}}
{\fancyplain{}{\bfseries\rightmark}}
{\fancyplain{}{\bfseries\thepage}}
\cfoot[]{}
%
%
% Earlier paragraphs were separated by some space
%
%\setlength{\parindent}{0pt}
%\setlength{\parskip}{1.5ex plus 0.7ex minus 0.6ex}

\newcommand{\manual}{\emph{\LaTeX{} Manual}~\cite{manual}}
\newcommand{\companion}{\emph{The \LaTeX{} Companion}~\cite{companion}}
\newcommand{\desgraupes}{\emph{\LaTeX{}, Apprentissage, guide et                            r�f�
rence}~\cite{desgraupes}}
\newcommand{\guide}{\emph{Local Guide}~\cite{local}}
[1ex]}
%
% Some commands for helping with INDEX creation
%
% \protect added because needed with french package. --mh
%
\newcommand{\bs}{\symbol{'134}}%Print backslash
%\newcommand{\bs}{\ensuremath{\mathtt{\backslash}}}%Print backslash
% Index entry for a command (\cih for hidden command index
\newcommand{\cih}[1]{%
\index{commandes!#1@\protect\texttt{\bs#1}}%
\index{#1@\protect\texttt{\hspace*{-1.2ex}\bs #1}}}
\newcommand{\ci}[1]{\cih{#1}\texttt{\bs#1}}
%Package
\newcommand{\pai}[1]{%
\index{extensions!#1@\protect\textsf{#1}}%
\index{#1@\protect\textsf{#1}}%
\textsf{#1}}
% Index entry for an environment
\newcommand{\ei}[1]{%
\index{environnements!\protect\texttt{#1}}%
\index{#1@\protect\texttt{#1}}%
\texttt{#1}}
% Indexentry for a word (Word inserted into the text)
\newcommand{\wi}[1]{\index{#1}#1}
%
% Typesetting Commands
%
\newenvironment{lscommand}%
\vskip -\parskip
\noindent%
\begin{tabular}{|l|}\hline\rule{0pt}{1em}\ignorespaces}%
minus 0.2ex}%
\vskip -\parskip}
%
% Type setting Code Fragments
%
\newenvironment{code}{\begin{quote}}{\end{quote}}
%
% Intro Environment
\newenvironment{intro}{\sffamily}{\vspace*{2ex minus 1.5ex}}

%
%
% Symbol Entry for Math Symbol Tables
%
\newcommand{\X}[1]{$#1$&\texttt{\string#1}\hspace*{1ex}}
% normal text ....
\newcommand{\SC}[1]{#1&\texttt{\string#1}\hspace*{1ex}}
% for accents in text mode
\newcommand{\A}[1]{#1&\texttt{\string#1}\hspace*{1ex}}
\newcommand{\B}[2]{#1#2&\texttt{\string#1{} #2}\hspace*{1ex}}

\newcommand{\W}[2]{$#1{#2}$&
\texttt{\string#1}\texttt{\string{\string#2\string}}\hspace*{1ex}}
\newcommand{\Y}[1]{$\big#1$ &\texttt{\string#1}}  %
% Mathsymbol Table
\newsavebox{\symbbox}
\newenvironment{symbols}[1]%
{\par\vspace*{2ex}
\renewcommand{\arraystretch}{1.1}
\begin{lrbox}{\symbbox}\hspace*{4ex}
\begin{tabular}{@{}#1@{}}}%
{\end{tabular}\end{lrbox}\makebox[\textwidth]

{\usebox{\symbbox}}\par\medskip}
%
% Special Prep for AMS Symbols Printout
% Should work if AMS is not available
%

% we have no PS versions of the rsfs fonts ... so this is a nogo for pdf
\ifx\pdfoutput\undefined % We're not running pdftex
\IfFileExists{mathrsfs.sty}
{\RequirePackage{mathrsfs}\let\MathRSFS\mathscr\let\mathscr\relax}{}
\fi
\IfFileExists{amssymb.sty}
{\let\noAMS\relax \RequirePackage{amssymb}}
{\def\noAMS{\endinput}\RequirePackage{latexsym}}
\IfFileExists{eucal.sty}
{\RequirePackage[mathscr]{eucal}}
{\IfFileExists{euscript.sty}
{\RequirePackage{euscript}}{}}
%\IfFileExists{eufrak.sty}
%  {\RequirePackage{eufrak}}{}
\IfFileExists{amsbsy.sty}
{\RequirePackage{amsbsy}}{}

%
% Print |--| to show a distance
%
\newcommand{\demowidth}[1]{\rule{0.3pt}{1.3ex}\rule{#1}   {0.3pt}\rule{0.3pt}{1.3ex}}
%
% un morceau pour hyperref
\def\realpageref#1{%
\@safe@activestrue%
\expandafter\real@setref\csname r@#1\endcsname\@secondoffive{#1}%
\@safe@activesfalse%
}

%
% --- example ----
% This is an environment to set LaTeX examples.
% On the left side the source text and on the
% right side the typeset text.
%
% \begin{example}
% \Large This is Large
% \end{example}
%
% This Part is stolen from the verbaim.sty by FMi
%
\newwrite\example@out
\newbox\exa@box
\newcounter{exacnt}
\setcounter{exacnt}{1}
\newlength{\savefboxrule}
\newlength{\savefboxsep}
\newlength{\outdent}
\setlength{\outdent}{2cm}

\newenvironment{example}%
{\begingroup% Lets Keep the Changes Local
\@bsphack
\immediate\openout \example@out \jobname.exa
\let\do\@makeother\dospecials\catcode\^^M\active
\def\verbatim@processline{%
\immediate\write\example@out{\the\verbatim@line}}%
\verbatim@start}%
{\immediate\closeout\example@out\@esphack\endgroup%
%
% And here comes my part. :-
%
\setbox\exa@box=\vbox{% This box is mainly for debugging
\stepcounter{exacnt}%
\setlength{\parindent}{0pt}%
% Page \lsspageref{exa:\theexacnt}
\expandafter\ifx\csname r@exa:\theexacnt\endcsname\relax\else
\ifx\pdfoutput\undefined % We're not running pdftex
\ifx\@pr@ORI\undefined % We're not using french package
\def\exa@page{\HyPsd@pageref{exa:\theexacnt}}%
else %
\def\exa@page{\@pr@ORI{exa:\theexacnt}}% french pageref is not a number
\fi %
\else %
\def\exa@page{\HyPsd@pageref{exa:\theexacnt}}%
\fi
\ifodd\exa@page\hspace*{0pt}\else\hspace*{-\outdent}\fi%
\fi
\makebox[\textwidth][l]{%
\raisebox{-\height}[0pt][\totalheight]{%
\begin{minipage}[t]{0.5\outdent+0.46\textwidth-3mm}%
\small\verbatiminput{\jobname.exa}
\end{minipage}}%
\hspace{5mm}%
\setlength{\savefboxrule}{\fboxrule}%
\setlength{\fboxrule}{0.1pt}%
\setlength{\savefboxsep}{\fboxsep}%
\setlength{\fboxsep}{3mm}%
\raisebox{-\height}[0pt][\totalheight]{%
\fbox{%
\begin{minipage}[t]{0.5\outdent+0.54\textwidth-2mm-2\fboxrule-2\fboxsep-0.7ex}%
\setlength{\fboxrule}{\savefboxrule}%
\setlength{\fboxsep}{\savefboxsep}%
\setlength{\fboxrule}{0.5pt}%
%\setlength{\parskip}{1ex plus 0.4ex minus 0.2ex}%
\setlength{\parskip}{0ex plus 0ex minus 0ex}%
\begin{trivlist}\item\small\input{\jobname.exa}
\end{trivlist}
\end{minipage}
}%
}%
}\label{exa:\theexacnt}%
} % end vbox
%\showthe\ht\exa@box
\par\addvspace{2.0ex plus 0.8ex minus 1ex}\vskip -\parskip
\noindent\box\exa@box
\par\addvspace{3.2ex plus 0.8ex minus 1ex}\vskip -\parskip
}
\newenvironment{lined}[1]%
{\begin{center}\begin{minipage}{#1}\hrule\medskip}
{\vspace{-1ex}\hrule \end{minipage}\end{center}}
% I want no headers on pages created by clearpage

\renewcommand{\cleardoublepage}
{\clearpage\if@twoside \ifodd\c@page\else
\hbox{}\thispagestyle{empty}\newpage\if@twocolumn\hbox{}\newpage\fi\fi\fi}

% French.sty redefined tilde. Grrr
\ifx\@tildeORI\undefined
\else
\let\tilde\@tildeORI
\fi

-
Adjust which part? The text that appears there? the (thickness, colour, length, etc. of) line that appears there? where the page number is placed? Which elements do you hope to have in the header, and which in the footer? – jon Mar 14 '14 at 4:37
@jon, I want to adjust the length of line in header/footer. – Med Mar 14 '14 at 4:40
Welcome to TeX.SX! Posting code that is a minimal working example would be helpful. – Adam Liter Mar 14 '14 at 4:49
Please keep in mind @Adam's remarks about making your code a minimum working example that demonstrates your problem. See How to write a MWE for tips on how to do this effectively. – cslstr Mar 14 '14 at 5:06
I think you are making the life complicated. Instead of using all those (mylayout and flshort) you may do the job yourself using geometry and fancyhdr packages. – Harish Kumar Mar 14 '14 at 6:19

The file flshort.sty contains a line

\addtolength{\headwidth}{\outdent}


which is the culprit of the long header line.

\addtolength{\headwidth}{-\outdent}


and you will have the expected behavior.

MWE:

\documentclass[12pt,a4paper,twoside]{book}
\usepackage[top=2.5cm,bottom=2.5cm,right=2.5cm,left=2.5cm]{geometry}
\usepackage[T1]{fontenc}
\usepackage[latin1]{inputenc}
\usepackage{flshort}

\usepackage[frenchb,english]{babel}

\usepackage{lipsum}  % just for the example

% Les ensembles math{\'e}matiques, utilisant l'extension amsfonts
\renewcommand{\footrulewidth}{1pt}

\begin{document}
\selectlanguage{frenchb}

\chapter{A chapter}
\section{A section}
\lipsum[1-15]
\end{document}


Output

-
hats off for reading and saving all those files and locationg the problem ;) – Harish Kumar Mar 14 '14 at 10:46
@HarishKumar Thanks :-) – karlkoeller Mar 14 '14 at 10:51
Thank you very much sir for your answer. – Med Mar 14 '14 at 15:34
@Med You're welcome. Happy to help. – karlkoeller Mar 14 '14 at 17:34
Thanks Karlkoeller :). – Med Mar 14 '14 at 17:58