sphinterpolate: 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/sphinterpolate - 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/sphinterpolate - from package: GMT

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

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