cpan: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/cpan - from package: perl-CPAN

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/cpan - from package: perl

You may install the required package with command apt-get install {package}

Error in other languages:
cpan: bevel nie gevind nie
cpan: comandă negăsită
cpan: comando não encontrado
cpan: commande introuvable
cpan: command not found
cpan: käsku ei ole
cpan: không tìm thấy lệnh
cpan: komanda nerasta
cpan: Kommando nicht gefunden.
cpan: kommandot finns inte
cpan: komut yok
cpan: nie znaleziono polecenia
cpan: níor aimsíodh an t-ordú
cpan: no se encontró la orden
cpan: no s'ha trobat l'ordre
cpan: opdracht niet gevonden
cpan: parancs nem található
cpan: perintah tidak ditemukan
cpan: príkaz nenájdený
cpan: příkaz nenalezen
cpan: команда не найдена
cpan: командата не е открита
cpan: 命令找不到
cpan: コマンドが見つかりません