ldiff: 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/ldiff - from package: rubygem-diff-lcs
/usr/lib/ruby/gems/1.8/gems/diff-lcs-1.1.2/bin/ldiff - from package: rubygem-diff-lcs

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

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