xcalc: 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 Debian possible default full paths are:

/usr/bin/xcalc - from package: x11-apps

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

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