Make alias from existing alias

Question

I have 2 separate files, which are both sourced from my .zshrc, one of them (the first one) is defining this alias:

alias wget='wget --hsts-file="$XDG_CACHE_HOME/wget-hsts"'

problem is that the other one, sourced after this one is also defining wget alias:

alias wget='wget -c'

I need to somehow ensure, that the second alias defines itself using the previous alias. I was thinking of using something like $(wget), but that just gets me into a recursive loop. Is there some good way to reference an already existing alias with the same name while defining a new one?

I was maybe thinking of somehow getting the content of the first alias and only concatenating that with my new flag so that it will build on the previous alias, I'd probably also have to do some handling to fall back to the real command if the command wasn't already aliased before.

Note: I know that I could just change the name of one of those aliases and reference it in the next one, but that's not what I'm asking for. Nor do I want to just simply define them as 1 alias manually. I want a way to actually automatically use the old alias definition when defining a new one, so that they get chained together .

Any idea how could I implement something like this? Or perhaps a better method to do something like this?

Answer 1

You can use the aliases hash table for this:

% zmodload -F zsh/parameter p:aliases
% alias wget='wget --hsts-file="$XDG_CACHE_HOME/wget-hsts"'
% alias wget="$aliases[wget] -c"
% alias
wget='wget --hsts-file="$XDG_CACHE_HOME/wget-hsts" -c'

I'd probably also have to do some handling to fall back to the real command if the command wasn't already aliased before

That can be achieved by using ${aliases[wget]:-wget}. Then, if $aliases[wget] is empty, the literal value wget will be used instead.

Answer 2

It can be done with some ugly parsing of the alias output:

$ alias foo='foo --first'
$ alias foo=$(alias foo | cut --delimiter== --fields=2 | head --bytes=-2 | tail --bytes=+2)' --second'
$ alias foo
alias foo='foo --first --second'

Of course, if alias ever prints the alias in any other format (multiple lines or different quotes) all bets are off. It also does not handle the case where the alias is not already set:

$ unalias foo
$ alias foo=$(alias foo | cut --delimiter== --fields=2 | head --bytes=-2 | tail --bytes=+2)' --second'
bash: alias: foo: not found
$ alias foo
alias foo=' --second'