Re: Next word of alias to alias that end with <blank> is not checked for alias

[Greg Wooledge]

On Thu, Jan 12, 2023 at 03:43:15AM +0000, anonymous4feedback@outlook.com wrote:
> Dear dir or madam,
> 
> For the following script:
> alias a1='echo '
> alias a2=a1
> alias foo=bar
> a2 foo
> bash outputs ‘foo’, instead of ‘bar’.
> 
> GNU bash, version 5.1.16(1)-release (x86_64-pc-linux-gnu) on archlinux as 
> windows subsystem for linux

First thing first: aliases are not used in scripts, unless bash is
invoked in POSIX mode, or the "expand_aliases" shopt is enabled.
So either this wasn't really a script (i.e. you ran these commands at
an interactive shell), or else this wasn't the *entire* script.

Second thing: the command in question here is "a2 foo", where a2 is
an alias.  But the a2 alias doesn't end with a space.  So there's no
reason to expect that the special "alias ends with a space" processing
would occur here.

If you used "a1 foo" then it *would* occur.

You're expecting an alias that aliases an alias to inherit the special
hacks of the alias that it's aliasing.  It doesn't.

If you want a2 to have the space-hack behavior, put a space after it.

Here's a working version:


unicorn:~$ cat foo
#!/bin/bash
shopt -s expand_aliases

alias a1='echo '
alias a2='a1 '
alias foo=bar

a1 foo one
a2 foo two
unicorn:~$ ./foo
bar one
bar two


In my opinion, the only bug here is in your script, not in bash.

Also my opinion: aliases are disabled in bash scripts for a reason.
They're ugly and horrible, and they don't promote good programming
practices.  Whatever you're trying to do here, I doubt aliases are
the best way to do it.  Consider using functions instead.