cpansign: 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/cpansign - from package: perl-Module-Signature

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

On Debian possible default full paths are:

/usr/bin/cpansign - from package: libmodule-signature-perl

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

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