jflex: 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/jflex - from package: jflex

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

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