zsh – How to Stack Shell Aliases

aliaszsh

In my .profile (sourced in sh emulation mode from my .zshrc) I have the following snippet:

if [ -f /usr/bin/pacmatic ]; then
    alias pacman=pacmatic
fi

# Colorized Pacman output
alias pacman="pacman --color auto"

However, the second alias always overrides the first:

% type pacman
pacman is an alias for pacman --color auto

How can I make it so that the second alias assignment "inherits" the first assignment, so that if /usr/bin/pacmatic exists, the alias becomes pacmatic --color auto?

I'm not averse to using functions instead of aliases, but I'd prefer it if the logic wasn't performed every time pacman is invoked (I want pacmatic checked for once, at shell startup, not every time pacman is run). I'd also prefer an sh-portable script, but if this isn't possible, you can use full zsh syntax.

(Yes, I'm aware that this could easily be solved by appending --color auto to the pacmatic alias. But I want to do it the Right Way™.)

I've tried Googling and looking through the manpages, but to no avail.

Best Answer

A shell alias behaves pretty similarly to a #define, i.e. redefining a shell alias would override the previous one.

I'm not sure what would be the Right Way^TM, but one approach would be making use a shell function that accepts parameters and using that to create an alias. Your code snippet could be rewritten as:

if [ -f /usr/bin/pacmatic ]; then
    pacman() { pacmatic "$@"; }
fi

# Colorized Pacman output
alias pacman="pacman --color auto"

Moreover, even if you were using different aliases and were trying to use one for defining the other, it would not work as aliases are not expanded in non-interactive mode by default. You need to enable it by setting expand_aliases:

shopt -s expand_aliases

Quoting from the manual:

   Aliases are not expanded when the shell is not interactive, unless  the
   expand_aliases  shell option is set using shopt (see the description of
   shopt under SHELL BUILTIN COMMANDS below).

Related Solutions

Resolve all aliases in a zsh command line

Note that Ctrl-Alt-E in bash does not only expand aliases. It also expands variables, command substitution (!), process substitution (!), arithmetic expand and removes quotes (it doesn't do filename generation (globbing) or tilde expansion).

It doesn't always manage to expand aliases. So while it has its uses, it's important to realise its outcome potentially changes the meaning of the command line, has side effects and is potentially dangerous.

For instance in:

$ a=';w' b=1
$ alias foo=bar
$ b=2; echo $b $a; cd /tmp/dir && for i do foo $(pwd) <(ls); done

If I press M-C-E here, that gives me:

$ b=2; echo 1 ;w; cd /tmp/dir && for i do foo / /dev/fd/63; done

Which gives me a completely different command line altogether (and imagine what would have happened if I had had rm -rf * instead of pwd above) and doesn't expand the foo alias.

With zsh, to build up on Gilles' note on aliases expanded inside functions, you could do:

expand-aliases() {
  unset 'functions[_expand-aliases]'
  functions[_expand-aliases]=$BUFFER
  (($+functions[_expand-aliases])) &&
    BUFFER=${functions[_expand-aliases]#$'\t'} &&
    CURSOR=$#BUFFER
}

zle -N expand-aliases
bindkey '\e^E' expand-aliases

That will expand the aliases only if the current command line is syntactically valid (so it doubles as a syntax checker).

Contrary to bash's M-C-E, it also resolves the aliases fully. For instance if you have:

$ alias ll='ls -l'; alias ls='ls --color'
$ ll

Will be expanded to:

$ ls --color -l

Note that it also canonicalises the syntax so things like:

$ for i (*) cmd $i; foo

will be changed to:

$ for i in *
        do
                cmd $i
        done
        foo

Bash – Forward aliases to child process

You shouldn't define aliases in /etc/zprofile or ~/.zprofile. These files is only loaded in login shells (“shells” meaning zsh of course). The proper place to define aliases is in /etc/zshrc or ~/.zshrc, which is read by all interactive shells.

To run zsh without loading /etc/zprofile, just run zsh with no option. The option -f tells zsh not to read configuration files at all, but since you want to read your alias definitions, that's not the right option. Since /etc/zprofile is only read by a login shell, just don't pass the -l option (and don't set a zeroth argument that begins with a dash).

Zsh has no option or environment variable to read one extra file on startup. If you want to prepare for that, you can add eval $ZSH_EXTRA_STARTUP_CODE to your .zshrc.

You can set the ZDOTDIR environment variable to make it read all of its user configuration files from a different directory, e.g. ZDOTDIR=/tmp/foo zsh reads /etc/zshenv, /tmp/foo/.zshenv, /etc/zshrc and /tmp/foo/zshrc. So to export aliases from the current instance to a child instance, you can run something like

tmp=$(mktemp -d)
alias -L >$tmp/.zshenv
echo ". ~/.zshenv; unset ZDOTDIR; rm -r ${(q)tmp}" >>$tmp/.zshenv
zsh

Best Answer

Related Solutions

Resolve all aliases in a zsh command line

Bash – Forward aliases to child process

Related Question