db5.3_sql: 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/db5.3_sql - from package: db5.3-sql-util

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

Error in other languages:
db5.3_sql: bevel nie gevind nie
db5.3_sql: comandă negăsită
db5.3_sql: comando não encontrado
db5.3_sql: commande introuvable
db5.3_sql: command not found
db5.3_sql: käsku ei ole
db5.3_sql: không tìm thấy lệnh
db5.3_sql: komanda nerasta
db5.3_sql: Kommando nicht gefunden.
db5.3_sql: kommandot finns inte
db5.3_sql: komut yok
db5.3_sql: nie znaleziono polecenia
db5.3_sql: níor aimsíodh an t-ordú
db5.3_sql: no se encontró la orden
db5.3_sql: no s'ha trobat l'ordre
db5.3_sql: opdracht niet gevonden
db5.3_sql: parancs nem található
db5.3_sql: perintah tidak ditemukan
db5.3_sql: príkaz nenájdený
db5.3_sql: příkaz nenalezen
db5.3_sql: команда не найдена
db5.3_sql: командата не е открита
db5.3_sql: 命令找不到
db5.3_sql: コマンドが見つかりません