gplc: 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 CentOS possible default full paths are:

/usr/bin/gplc - from package: gprolog
/usr/lib64/gprolog-1.3.1/bin/gplc - from package: gprolog

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/lib/gprolog-iso/bin/gplc - from package: gprolog

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

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