nl: 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/nl - from package: coreutils

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

On Debian possible default full paths are:

/usr/bin/nl - from package: coreutils

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

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