gpre: 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/gpre - from package: firebird

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

On Debian possible default full paths are:

/usr/bin/gpre - from package: firebird2.5-classic-common
/usr/bin/gpre - from package: firebird2.5-super

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

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