update-perl-sax-parsers: 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 Debian possible default full paths are:

/usr/bin/update-perl-sax-parsers - from package: libxml-sax-perl

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