express: 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/express - from package: nodejs-express
/usr/lib/node_modules/express/bin/express - from package: nodejs-express

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

On Debian possible default full paths are:

/usr/bin/express - from package: node-express-generator
/usr/lib/nodejs/express-generator/bin/express - from package: node-express-generator

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

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