ninja-ide: 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/ninja-ide - from package: ninja-ide

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

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