hexchat: 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/hexchat - from package: hexchat

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

On Debian possible default full paths are:

/usr/bin/hexchat - from package: hexchat

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

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