checkdigits.pl: command not found

Have You tried accessing the binary with the full path?

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/checkdigits.pl - from package: perl-Algorithm-CheckDigits

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