graph.pl: 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 Debian possible default full paths are:

/usr/share/doc/librdf-trine-perl/examples/bin/graph.pl - from package: librdf-trine-perl

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

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