glsl-preprocessor-comments: 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 CentOS possible default full paths are:

/usr/lib64/piglit/bin/glsl-preprocessor-comments - from package: piglit

You may install the required package with command yum install {package}

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