include-what-you-use: 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/include-what-you-use - from package: iwyu

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

On Debian possible default full paths are:

/usr/bin/include-what-you-use - from package: iwyu

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

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