qucsator: 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/qucsator - from package: qucs

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

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