gap5_cmd: 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/lib/staden/bin/gap5_cmd - from package: staden

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

Error in other languages:
gap5_cmd: bevel nie gevind nie
gap5_cmd: comandă negăsită
gap5_cmd: comando não encontrado
gap5_cmd: commande introuvable
gap5_cmd: command not found
gap5_cmd: käsku ei ole
gap5_cmd: không tìm thấy lệnh
gap5_cmd: komanda nerasta
gap5_cmd: Kommando nicht gefunden.
gap5_cmd: kommandot finns inte
gap5_cmd: komut yok
gap5_cmd: nie znaleziono polecenia
gap5_cmd: níor aimsíodh an t-ordú
gap5_cmd: no se encontró la orden
gap5_cmd: no s'ha trobat l'ordre
gap5_cmd: opdracht niet gevonden
gap5_cmd: parancs nem található
gap5_cmd: perintah tidak ditemukan
gap5_cmd: príkaz nenájdený
gap5_cmd: příkaz nenalezen
gap5_cmd: команда не найдена
gap5_cmd: командата не е открита
gap5_cmd: 命令找不到
gap5_cmd: コマンドが見つかりません