回复: Possible bug in bash

[address@hidden]

al is an alias defined to be a space. The line is intended to be expanded to 
for foo in v. But in posix mode bash expands this to for bar in v.
foo is an alias for bar, but it should not be substituted in this context.

alias al=' '


发件人: Write2Mark1<mailto:write2mark1@gmail.com>
发送时间: 2023年1月17日 20:37
收件人: Anonymous4Feedback<mailto:anonymous4feedback@outlook.com>
主题: Re: 回复: Possible bug in bash

What does this do  pls


al for foo in v


On Jan 16, 2023 at 11:26 PM, 
<Anonymous4Feedback<mailto:anonymous4feedback@outlook.com>> wrote:

I am sorry I made a mistake in the first email. Bash printed foo= bar=v and all 
other shells printed foo=v bar=. It turns out I am using --posix to enable 
alias in bash, and that’s what makes the difference.



# file test

shopt -s expand_aliases 2>/dev/null

alias al=' '

alias foo=bar

al for foo in v

do echo foo=$foo bar=$bar

done



$ bash ./test

foo=v bar=

$ bash --posix ./test

foo= bar=v





发件人: Chet Ramey<mailto:chet.ramey@case.edu>

发送时间: 2023年1月17日 3:41

收件人: anonymous4feedback@outlook.com<mailto:anonymous4feedback@outlook.com>; 
bug-bash@gnu.org<mailto:bug-bash@gnu.org>

抄送: chet.ramey@case.edu<mailto:chet.ramey@case.edu>

主题: Re: Possible bug in bash



On 1/15/23 7:42 AM, anonymous4feedback@outlook.com wrote:

> For the follow script

> alias al=' '

> alias foo=bar

> al for foo in v

> do echo foo=$foo bar=$bar

> done

> bash (version 5.1.16) prints foo=v bar=, while all other shells I tested 
> (dash, ksh, zsh, and yash) all prints foo= bar=v.



That's strange. I get the same results you do for bash, but I tried the

same shells you did and got the same results as bash (for different

reasons, I suspect).



$ cat x4

shopt -s expand_aliases 2>/dev/null

alias al=' '

alias foo=bar

al for foo in v

do echo foo=$foo bar=$bar

done

$ ./bash ./x4

foo=v bar=

$ dash ./x4

foo=v bar=

$ ksh93 ./x4

foo=v bar=

$ yash ./x4

foo=v bar=

$ mksh ./x4

foo=v bar=

$ zsh ./x4

foo=v bar=

$ ./bash --version

GNU bash, version 5.2.15(54)-maint (x86_64-apple-darwin21.6.0)

Copyright (C) 2022 Free Software Foundation, Inc.

License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>



This is free software; you are free to change and redistribute it.

There is NO WARRANTY, to the extent permitted by law.





> Apparently bash substitutes foo for bar in line 3 because the previous alias 
> al ends with a space. But it is unintuitive that the word after for is 
> checked for alias.



This is the opposite of what happens. In default mode, which you're

probably using, bash checks `for' for aliases, and, finding none, stops

checking. The other shells probably *don't* check whether `for' has an

alias, because POSIX says reserved words can't be alias expanded ("However,

reserved words in correct grammatical context shall not be candidates for

alias substitution.") Either way, the `check the next word for alias

expansion' flag gets turned off.



> According to the posix standard,

> If the value of the alias replacing the word ends in a <blank>, the shell 
> shall check the next command word for alias substitution; this process shall 
> continue until a word is found that is not a valid alias or an alias value 
> does not end in a <blank>.





> But “command word” is not defined. It is ambiguous whether “for” in this 
> context is a command word, or whether tokens other than command word is 
> allowed between the first alias and the next command word.



`Command word' refers to the previous paragraph: since alias expansion is

attempted on "a resulting word that is identified to be the command name

word of a simple command," the "next command word" is presumably the word

following that one.



>

> The same is true for case

> alias al=' '

> alias foo=bar

> al case foo in foo) echo foo;; bar) echo bar;; esac



Everybody prints `foo'.



--

``The lyf so short, the craft so long to lerne.'' - Chaucer

                 ``Ars longa, vita brevis'' - Hippocrates

Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/