gcalctool: 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/gcalctool - from package: gcalctool

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

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