gifview: 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/gifview - from package: gifview

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

On Debian possible default full paths are:

/usr/bin/gifview - from package: gifsicle

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

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