git-cal: 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/git-cal - from package: git-cal

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