gdal_landsat_pansharp: 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/gdal_landsat_pansharp - from package: dans-gdal-scripts

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

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