txt2las: command not found

Have You tried accessing the binary with the full path?

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/txt2las - from package: liblas-bin

You may install the required package with command apt-get install {package}
Error in other languages:
txt2las: bevel nie gevind nie
txt2las: comandă negăsită
txt2las: comando não encontrado
txt2las: commande introuvable
txt2las: command not found
txt2las: käsku ei ole
txt2las: không tìm thấy lệnh
txt2las: komanda nerasta
txt2las: Kommando nicht gefunden.
txt2las: kommandot finns inte
txt2las: komut yok
txt2las: nie znaleziono polecenia
txt2las: níor aimsíodh an t-ordú
txt2las: no se encontró la orden
txt2las: no s'ha trobat l'ordre
txt2las: opdracht niet gevonden
txt2las: parancs nem található
txt2las: perintah tidak ditemukan
txt2las: príkaz nenájdený
txt2las: příkaz nenalezen
txt2las: команда не найдена
txt2las: командата не е открита
txt2las: 命令找不到
txt2las: コマンドが見つかりません