pgmslice: 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/pgmslice - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pgmslice - from package: netpbm

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

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