tcpclient: 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/tcpclient - from package: ucspi-tcp-ipv6
/usr/bin/tcpclient - from package: ucspi-tcp

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

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