eric5_qregularexpression: 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 Debian possible default full paths are:

/usr/bin/eric5_qregularexpression - from package: eric

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

Error in other languages:
eric5_qregularexpression: bevel nie gevind nie
eric5_qregularexpression: comandă negăsită
eric5_qregularexpression: comando não encontrado
eric5_qregularexpression: commande introuvable
eric5_qregularexpression: command not found
eric5_qregularexpression: käsku ei ole
eric5_qregularexpression: không tìm thấy lệnh
eric5_qregularexpression: komanda nerasta
eric5_qregularexpression: Kommando nicht gefunden.
eric5_qregularexpression: kommandot finns inte
eric5_qregularexpression: komut yok
eric5_qregularexpression: nie znaleziono polecenia
eric5_qregularexpression: níor aimsíodh an t-ordú
eric5_qregularexpression: no se encontró la orden
eric5_qregularexpression: no s'ha trobat l'ordre
eric5_qregularexpression: opdracht niet gevonden
eric5_qregularexpression: parancs nem található
eric5_qregularexpression: perintah tidak ditemukan
eric5_qregularexpression: príkaz nenájdený
eric5_qregularexpression: příkaz nenalezen
eric5_qregularexpression: команда не найдена
eric5_qregularexpression: командата не е открита
eric5_qregularexpression: 命令找不到
eric5_qregularexpression: コマンドが見つかりません