zabbix_get: 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/zabbix_get - from package: zabbix20
/usr/bin/zabbix_get - from package: zabbix22
/usr/bin/zabbix_get - from package: zabbix-proxy
/usr/bin/zabbix_get - from package: zabbix-server

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

On Debian possible default full paths are:

/usr/bin/zabbix_get - from package: zabbix-proxy-mysql
/usr/bin/zabbix_get - from package: zabbix-proxy-pgsql
/usr/bin/zabbix_get - from package: zabbix-proxy-sqlite3
/usr/bin/zabbix_get - from package: zabbix-server-mysql
/usr/bin/zabbix_get - from package: zabbix-server-pgsql

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

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