How do I to make this header text takes this form Chapitre 1. Spécification des besoins ?

EDIT : Transformation : CHAPITRE 1. SPECIFICATION DES BESOINS >> Chapitre 1. Spécification des besoins

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Should this be on every page or just on even/odd ones? –  Gonzalo Medina Feb 15 at 17:01
@GonzaloMedina, left header of each page. –  dgs Feb 15 at 17:04

You can use the fancyhdr package:

\documentclass{book}
\usepackage[french]{babel}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{fancyhdr}
\usepackage{lipsum}

\pagestyle{fancy}

\fancyhf{}
\fancyfoot[C]{\thepage}

\begin{document}

\chapter{Spécification des besoin}
\lipsum[1-40]

\end{document}


Since no information was given about the position of the page number, I placed it at the center in the footer, but this can be changed as needed.

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I've edited my post. –  dgs Feb 15 at 17:13
@user3289501 please see my updated answer. –  Gonzalo Medina Feb 15 at 17:16
Chapitre 1. Spécification des besoins –  dgs Feb 15 at 17:18
@user3289501 Yes, see the new edit. –  Gonzalo Medina Feb 15 at 17:19
Oh, come on. +1 for being quicker in modifying the answer. You can always upvote another question of mine ;-) –  karlkoeller Feb 15 at 17:37