regression_tests.sh: 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/share/doc/r-cran-qtl/examples/bin/scripts/regression_tests.sh - from package: r-cran-qtl

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

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