x3270if: 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/x3270if - from package: x3270

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

Error in other languages:
x3270if: bevel nie gevind nie
x3270if: comandă negăsită
x3270if: comando não encontrado
x3270if: commande introuvable
x3270if: command not found
x3270if: käsku ei ole
x3270if: không tìm thấy lệnh
x3270if: komanda nerasta
x3270if: Kommando nicht gefunden.
x3270if: kommandot finns inte
x3270if: komut yok
x3270if: nie znaleziono polecenia
x3270if: níor aimsíodh an t-ordú
x3270if: no se encontró la orden
x3270if: no s'ha trobat l'ordre
x3270if: opdracht niet gevonden
x3270if: parancs nem található
x3270if: perintah tidak ditemukan
x3270if: príkaz nenájdený
x3270if: příkaz nenalezen
x3270if: команда не найдена
x3270if: командата не е открита
x3270if: 命令找不到
x3270if: コマンドが見つかりません