tre-agrep: 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/tre-agrep - from package: tre-agrep

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

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