usrp_flex: 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 Debian possible default full paths are:

/usr/bin/usrp_flex - from package: gnuradio

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

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