bashrc + why source not refresh the .bashrc file

Question

we add the following line to bashrc file

alias reboot="echo you not allowed to do reboot on this machine - sorry"

so we get

more ~/.bashrc

# .bashrc

# User specific aliases and functions

alias rm='rm -i'
alias cp='cp -i'
alias mv='mv -i'

# Source global definitions
if [ -f /etc/bashrc ]; then
        . /etc/bashrc
fi


alias reboot="echo you not allowed to do reboot on this machine - sorry"

then we did

source ~/.bashrc

and indeed when we do

reboot

we got

you not allowed to do reboot on this machine - sorry

but when we want to back to real reboot , we removed the line --> alias reboot="echo you not allowed to do reboot on this machine - sorry"

as the following:

# .bashrc

# User specific aliases and functions

alias rm='rm -i'
alias cp='cp -i'
alias mv='mv -i'

# Source global definitions
if [ -f /etc/bashrc ]; then
        . /etc/bashrc
fi

and we refresh the bashrc

source ~/.bashrc

but we still get the old alias when we try to reboot:

 you not allowed to do reboot on this machine - sorry

what we are missing here?

another example with function

echo '
function reboot
{
echo "ERROR reboot command not allowed on this machine"
return 1
}
' >>/root/.bashrc

with example above we cant to do unalias

Answer 1

Sourcing ~/.bashrc does not magically reset all settings. The file is just a bunch of commands to be executed. If they are executed in a clean shell then you will get what you expect.

But if the alias has already been defined, the lack of it in the file will not unalias it. Think about it: if you executed the commands from the file by hand, none would affect the already defined alias. There is no unalias reboot in the file. Sourcing ~/.bashrc is exactly executing the commands, only not "by hand".

Do not treat .bashrc as a file that holds current settings for the shell. It is meant to be sourced once in a clean shell, automatically. People sometimes source it again manually and it works* if they add something, because the added thing gets executed. A removed thing cannot be executed or magically reverted. Start a new shell and let .bashrc do its job in the way it's designed for.

Note it's totally easy to bypass an alias or a function. The alias or the function is not a good way to disallow rebooting.

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^{* It works with possible side effects from executing old things for the second time.}