tgif: 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/tgif - from package: tgif

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

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