fst-compact: 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/fst-compact - from package: sfst

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

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