gnuplot-minimal: 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/gnuplot-minimal - from package: gnuplot-minimal

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

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