ipcalc: 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:

/bin/ipcalc - from package: initscripts

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

On Debian possible default full paths are:

/usr/bin/ipcalc - from package: ipcalc

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

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