restclient: 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/restclient - from package: rubygem-rest-client
/usr/lib/ruby/gems/1.8/gems/rest-client-1.6.1/bin/restclient - from package: rubygem-rest-client

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

On Debian possible default full paths are:

/usr/bin/restclient - from package: ruby-rest-client

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

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