wannier_plot.x: 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/bin/wannier_plot.x - from package: quantum-espresso

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

On Debian possible default full paths are:

/usr/bin/wannier_plot.x - from package: quantum-espresso

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

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