mewcat: 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/mewcat - from package: mew-beta-bin
/usr/bin/mewcat - from package: mew-bin

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

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