greenspline: 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/greenspline - from package: GMT

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

On Debian possible default full paths are:

/usr/lib/gmt/bin/greenspline - from package: GMT

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

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