httpclient: 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 CentOS possible default full paths are:

/usr/bin/HttpClient - from package: pki-java-tools
/usr/lib/ruby/gems/1.8/gems/httpclient-2.4.0/bin/httpclient - from package: rubygem-httpclient

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/HttpClient - from package: ruby-httpclient

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

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