regexp-assemble: 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/bin/regexp-assemble - from package: libregexp-assemble-perl

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

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