macptopbm: 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/macptopbm - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/macptopbm - from package: netpbm

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

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