wvgain: 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/wvgain - from package: wavpack

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

On Debian possible default full paths are:

/usr/bin/wvgain - from package: wavpack

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

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