jirb_swing: 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/lib/jruby/bin/jirb_swing - from package: jruby

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

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