stg-show-old: 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

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/bin/stg-show-old - from package: stgit-contrib

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