avr-ar: 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/avr-ar - from package: avr-binutils

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

On Debian possible default full paths are:

/usr/bin/avr-ar - from package: binutils-avr

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

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