fldiff: 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/fldiff - from package: fldiff

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

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