How do I expand an alias defined when using zsh -c?
% zsh -c 'setopt aliases complete_aliases; alias d=date; d'
zsh:1: command not found: d
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1 Answer
Use eval to force the zsh to parse the alias after the code has been read in:
zsh -c 'setopt aliases complete_aliases; alias d=date; eval d'
In this case, d will never expand, so doesn't need to be quoted.
In general you should properly quote all arguments to eval.
man zshmisc says:
There is a commonly encountered problem with aliases illustrated by the following code: alias echobar='echo bar'; echobar This prints a message that the command echobar could not be found. This happens because aliases are expanded when the code is read in; the entire line is read in one go, so that when echobar is executed it is too late to expand the newly defined alias. This is often a problem in shell scripts, functions, and code executed with `source' or `.'. Consequently, use of functions rather than aliases is recommended in non-interactive code.
5 Comments
chepner
Better yet, don't use an alias; define a function. A function definition is an ordinary command, and so is guaranteed to be defined before you attempt to use it, even on the same command line.
zsh -c 'd() date; d.
Tom Hale
@chepner Generally good advice, but in this case I'm writing a generic alias expander for use in
nohup alias, nice alias, chrt alias etc.
Xunnamius
Had to scour the internet to find this answer, so THANK YOU! As of 2022, it seems this can be reduced to
zsh -c 'alias d=date; eval d'.
Chris
Another thank you from 2022! In my case I'm trying to use
viddy (which is just like watch) and to watch the output of a shell alias defined in my ~/.zshrc. For this to work in viddy this does the trick: viddy --shell zsh "source ~/.zshrc; eval ll" (with the alias ll in that case). You'd think I could do zsh --interactive but that causes the shell to exit weirdly for reasons I don't yet grasp.
Guido Tarsia
big thanks from me as well, spared me from fake interactive shell damnation