shorten: command not found

Have You tried accessing the binary with the full path?

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/shorten - from package: perl-WWW-Shorten

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