hexmerge: 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 Debian possible default full paths are:

/usr/bin/hexmerge - from package: unifont-bin

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

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