xshell.sh: 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/xshell.sh - from package: xvile

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

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