Where does Bash's “not found” message come from?

Question

If I type an invalid command in Bash, I get:

$ asdf
asdf: not found

I've been led to believe the "not found" message comes from a fallback executable that Bash calls when it can't find the command you enter. What is the name and path of this executable?

Answer 1

Further to Rena's answer, yes it is a function -- and you can replace it!

This link details how to do it. Fascinating post, actually. Just in time for April Fool's! sl command anyone?

Generously lifted from the linked article (for posterity) is this code snippet on placing this function in your .bashrc on an openSUSE platform:

command_not_found_handle() {

    export TEXTDOMAIN=command-not-found

    local cmd state rest
    local -i pid ppid pgrp session tty_nr tpgid

    # do not run when inside Midnight Commander or within a Pipe
    if test -n "$MC_SID" -o ! -t 1 ; then
        echo $"$1: command not found"
        return 127
    fi

    # do not run when within a subshell
    read pid cmd state ppid pgrp session tty_nr tpgid rest  < /proc/self/stat
    if test $$ -eq $tpgid ; then
        echo "$1: command not found"
        return 127
    fi

    # test for /usr/sbin and /sbin
    if test -x "/usr/sbin/$1" -o -x "/sbin/$1" ; then
        if test -x "/usr/sbin/$1" ; then prefix='/usr' ; else prefix='' ; fi
        echo $"Absolute path to '$1' is '$prefix/sbin/$1', so running it may require superuser privileges (eg. root)."
        return 127
    fi

    if test -n "$COMMAND_NOT_FOUND_AUTO" ; then
        # call command-not-found directly
        test -x /usr/bin/python && test -x /usr/bin/command-not-found && /usr/bin/python /usr/bin/command-not-found "$1" zypp
    else
        # print only info about command-not-found
        echo -e $"If '$1' is not a typo you can use command-not-found to lookup the package that contains it, like this:\n    cnf $1"
    fi

    return 127
}

Answer 2

It is issued by bash itself. Try

strings `which bash` | fgrep found

Answer 3

Did some further digging and found out it's not an executable, but a function, command_not_found_handle() within Bash.