gems-client: 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/gems-client - from package: gems

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

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