hdf2gif: 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/hdf2gif - from package: hdf

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

On Debian possible default full paths are:

/usr/bin/hdf2gif - from package: hdf4-tools

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

Error in other languages:
hdf2gif: bevel nie gevind nie
hdf2gif: comandă negăsită
hdf2gif: comando não encontrado
hdf2gif: commande introuvable
hdf2gif: command not found
hdf2gif: käsku ei ole
hdf2gif: không tìm thấy lệnh
hdf2gif: komanda nerasta
hdf2gif: Kommando nicht gefunden.
hdf2gif: kommandot finns inte
hdf2gif: komut yok
hdf2gif: nie znaleziono polecenia
hdf2gif: níor aimsíodh an t-ordú
hdf2gif: no se encontró la orden
hdf2gif: no s'ha trobat l'ordre
hdf2gif: opdracht niet gevonden
hdf2gif: parancs nem található
hdf2gif: perintah tidak ditemukan
hdf2gif: príkaz nenájdený
hdf2gif: příkaz nenalezen
hdf2gif: команда не найдена
hdf2gif: командата не е открита
hdf2gif: 命令找不到
hdf2gif: コマンドが見つかりません