curl: 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/curl - from package: curl

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

On Debian possible default full paths are:

/usr/bin/curl - from package: curl

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

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