aliases in zsh -c and eval

aliases in zsh -c and eval

[Stephane Chazelas]

Hiya,

it looks like aliases defined in `zsh -c` are not expanded in
there:

$ zsh -c 'alias foo=echo
foo bar'
zsh:2: command not found: foo

Those defined for instance in ~/.zshenv are expanded. And:

$ zsh -c 'alias foo=echo
eval foo bar'
bar

It looks like zsh is the only one out here. (with bash you need
bash -O expand_aliases).

Same with eval:

$ (eval 'alias foo=echo
subsh quote> foo bar')
zsh: command not found: foo
$ (eval 'alias foo=echo
eval foo bar')
bar

This time, ksh93 does behave like zsh.

-- 
Stephane

Re: aliases in zsh -c and eval

[Stephane Chazelas]

2014-11-27 21:22:22 +0000, Stephane Chazelas:
> Hiya,
> 
> it looks like aliases defined in `zsh -c` are not expanded in
> there:
> 
> $ zsh -c 'alias foo=echo
> foo bar'
> zsh:2: command not found: foo
> 
> Those defined for instance in ~/.zshenv are expanded. And:
> 
> $ zsh -c 'alias foo=echo
> eval foo bar'
> bar
> 
> It looks like zsh is the only one out here. (with bash you need
> bash -O expand_aliases).
> 
> Same with eval:
> 
> $ (eval 'alias foo=echo
> subsh quote> foo bar')
> zsh: command not found: foo
> $ (eval 'alias foo=echo
> eval foo bar')
> bar
> 
> This time, ksh93 does behave like zsh.
[...]

For completeness:

$ cat > a
alias foo=echo
foo bar
$ zsh a
bar
$ zsh -c '. ./a'
bar
$ zsh -c 'eval "$(cat ./a)"'
(eval):2: command not found: foo
$ ksh a
bar
$ ksh -c '. ./a'
ksh: .[2]: foo: not found [No such file or directory]

ksh worse this time.

-- 
Stephane

Re: aliases in zsh -c and eval

[Mikael Magnusson]

On Thu, Nov 27, 2014 at 10:22 PM, Stephane Chazelas
<stephane.chazelas@gmail.com> wrote:
> Hiya,
>
> it looks like aliases defined in `zsh -c` are not expanded in
> there:
>
> $ zsh -c 'alias foo=echo
> foo bar'
> zsh:2: command not found: foo
>
> Those defined for instance in ~/.zshenv are expanded. And:
>
> $ zsh -c 'alias foo=echo
> eval foo bar'
> bar
>
> It looks like zsh is the only one out here. (with bash you need
> bash -O expand_aliases).
>
> Same with eval:
>
> $ (eval 'alias foo=echo
> subsh quote> foo bar')
> zsh: command not found: foo
> $ (eval 'alias foo=echo
> eval foo bar')
> bar
>
> This time, ksh93 does behave like zsh.
>
> --
> Stephane

This is documented near the start of the "Aliasing" section of the manpage.

       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.

-- 
Mikael Magnusson

Re: aliases in zsh -c and eval

[Peter Stephenson]

On Thu, 27 Nov 2014 21:22:22 +0000
Stephane Chazelas <stephane.chazelas@gmail.com> wrote:
> it looks like aliases defined in `zsh -c` are not expanded in
> there:
> 
> $ zsh -c 'alias foo=echo
> foo bar'
> zsh:2: command not found: foo

Yes, this is normal in text which is input in one go, as documented in
"Aliasing" in the grammar section of the manual, see below.  This is
inevitable as the whole thing is passed to the shell as a single string,
so it's input as a single string.  Presumably some other shells have
input factored in such a way that strings and files are considered more
similarly.


There is a commonly encountered problem with aliases
illustrated by the following code:

example(alias echobar='echo bar'; echobar)

This prints a message that the command tt(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 tt(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 `tt(source)'
or `tt(.)'.  Consequently, use of functions rather than aliases is
recommended in non-interactive code.

pws