double: 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/double - from package: plotutils

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

On Debian possible default full paths are:

/usr/bin/double - from package: plotutils

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

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