ris2xml: 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:

/usr/bin/ris2xml - from package: bibutils

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

On Debian possible default full paths are:

/usr/bin/ris2xml - from package: bibutils

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

Error in other languages:
ris2xml: bevel nie gevind nie
ris2xml: comandă negăsită
ris2xml: comando não encontrado
ris2xml: commande introuvable
ris2xml: command not found
ris2xml: käsku ei ole
ris2xml: không tìm thấy lệnh
ris2xml: komanda nerasta
ris2xml: Kommando nicht gefunden.
ris2xml: kommandot finns inte
ris2xml: komut yok
ris2xml: nie znaleziono polecenia
ris2xml: níor aimsíodh an t-ordú
ris2xml: no se encontró la orden
ris2xml: no s'ha trobat l'ordre
ris2xml: opdracht niet gevonden
ris2xml: parancs nem található
ris2xml: perintah tidak ditemukan
ris2xml: príkaz nenájdený
ris2xml: příkaz nenalezen
ris2xml: команда не найдена
ris2xml: командата не е открита
ris2xml: 命令找不到
ris2xml: コマンドが見つかりません