merge: 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/merge - from package: rcs

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

On Debian possible default full paths are:

/usr/bin/merge - from package: rcs

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

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