pg_tapgen: 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/bin/pg_tapgen - from package: libtap-parser-sourcehandler-pgtap-perl

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

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