xclips: 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/xclips - from package: clips-xclips

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

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