gnuplot-wx: 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-wx - from package: gnuplot

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

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