pnmshear: 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/pnmshear - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pnmshear - from package: netpbm

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

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