show: 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/mh/show - from package: nmh

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

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