c_oper1.o: 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/x86_64-linux-gnu/gap/bin/c_oper1.o - from package: gap-dev

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

Error in other languages:
c_oper1.o: bevel nie gevind nie
c_oper1.o: comandă negăsită
c_oper1.o: comando não encontrado
c_oper1.o: commande introuvable
c_oper1.o: command not found
c_oper1.o: käsku ei ole
c_oper1.o: không tìm thấy lệnh
c_oper1.o: komanda nerasta
c_oper1.o: Kommando nicht gefunden.
c_oper1.o: kommandot finns inte
c_oper1.o: komut yok
c_oper1.o: nie znaleziono polecenia
c_oper1.o: níor aimsíodh an t-ordú
c_oper1.o: no se encontró la orden
c_oper1.o: no s'ha trobat l'ordre
c_oper1.o: opdracht niet gevonden
c_oper1.o: parancs nem található
c_oper1.o: perintah tidak ditemukan
c_oper1.o: príkaz nenájdený
c_oper1.o: příkaz nenalezen
c_oper1.o: команда не найдена
c_oper1.o: командата не е открита
c_oper1.o: 命令找不到
c_oper1.o: コマンドが見つかりません