s3ls: 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/s3ls - from package: libnet-amazon-s3-tools-perl

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

Error in other languages:
s3ls: bevel nie gevind nie
s3ls: comandă negăsită
s3ls: comando não encontrado
s3ls: commande introuvable
s3ls: command not found
s3ls: käsku ei ole
s3ls: không tìm thấy lệnh
s3ls: komanda nerasta
s3ls: Kommando nicht gefunden.
s3ls: kommandot finns inte
s3ls: komut yok
s3ls: nie znaleziono polecenia
s3ls: níor aimsíodh an t-ordú
s3ls: no se encontró la orden
s3ls: no s'ha trobat l'ordre
s3ls: opdracht niet gevonden
s3ls: parancs nem található
s3ls: perintah tidak ditemukan
s3ls: príkaz nenájdený
s3ls: příkaz nenalezen
s3ls: команда не найдена
s3ls: командата не е открита
s3ls: 命令找不到
s3ls: コマンドが見つかりません