gif2x11: 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/gif2x11 - from package: giflib-utils

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

Error in other languages:
gif2x11: bevel nie gevind nie
gif2x11: comandă negăsită
gif2x11: comando não encontrado
gif2x11: commande introuvable
gif2x11: command not found
gif2x11: käsku ei ole
gif2x11: không tìm thấy lệnh
gif2x11: komanda nerasta
gif2x11: Kommando nicht gefunden.
gif2x11: kommandot finns inte
gif2x11: komut yok
gif2x11: nie znaleziono polecenia
gif2x11: níor aimsíodh an t-ordú
gif2x11: no se encontró la orden
gif2x11: no s'ha trobat l'ordre
gif2x11: opdracht niet gevonden
gif2x11: parancs nem található
gif2x11: perintah tidak ditemukan
gif2x11: príkaz nenájdený
gif2x11: příkaz nenalezen
gif2x11: команда не найдена
gif2x11: командата не е открита
gif2x11: 命令找不到
gif2x11: コマンドが見つかりません