xml2bib: 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/xml2bib - from package: bibutils

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

On Debian possible default full paths are:

/usr/bin/xml2bib - from package: bibutils

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

Error in other languages:
xml2bib: bevel nie gevind nie
xml2bib: comandă negăsită
xml2bib: comando não encontrado
xml2bib: commande introuvable
xml2bib: command not found
xml2bib: käsku ei ole
xml2bib: không tìm thấy lệnh
xml2bib: komanda nerasta
xml2bib: Kommando nicht gefunden.
xml2bib: kommandot finns inte
xml2bib: komut yok
xml2bib: nie znaleziono polecenia
xml2bib: níor aimsíodh an t-ordú
xml2bib: no se encontró la orden
xml2bib: no s'ha trobat l'ordre
xml2bib: opdracht niet gevonden
xml2bib: parancs nem található
xml2bib: perintah tidak ditemukan
xml2bib: príkaz nenájdený
xml2bib: příkaz nenalezen
xml2bib: команда не найдена
xml2bib: командата не е открита
xml2bib: 命令找不到
xml2bib: コマンドが見つかりません