csharp: 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/csharp - from package: mono-core

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

On Debian possible default full paths are:

/usr/bin/csharp - from package: mono-csharp-shell

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

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