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From: Janis Papanagnou <janis_papanagnou+ng@hotmail.com>
Newsgroups: comp.unix.shell
Subject: Re: Default PATH setting - reduce to something more sensible?
Date: Fri, 24 Jan 2025 11:13:00 +0100
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On 23.01.2025 23:46, Keith Thompson wrote:
> Kaz Kylheku <643-408-1753@kylheku.com> writes:
> [...]
>> The obvious situation is double quotes. Inside double quotes, parameter
>> expansion happens, but not tilde expansion (not to mention pathname
>> expansion (globbing) and perhaps some other things).
>>
>> So this won't work:
>>
>>  PATH="$PATH:~/bin"
>>
>>> Sorry I don't have details, but it is true nonetheless.
>>
>> There they are.
> [...]
> 
> In fact it probably will *partially* work.  As I mentioned elsethread,
> bash expands a leading ~ (or even ~username) in an element of $PATH when
> executing a command.

Interpretation of any _leading_ '~' is the documented behavior for
tilde expansion.

> 
> But if you run a program from the command line that invokes another
> program (say, a C program that calls system()), it won't treat that
> element of $PATH the same way.

I think the point is that the _shell_ expands the expression.

Whether you do PATH="~" or PATH='~' or PATH=\~ , in all cases you have
defined a variable value that contains '~', a tilde. Not an expanded
tilde-expression. So if you 'exec' a command that PATH variable (with
the literal tilde) will get passed to the executable environment (and
no shell interpretation takes place).

Use PATH=~ instead if you want it expanded.

> 
> For this and other reasons, though you *can* have a literal ~ in $PATH
> in bash, it's best to avoid it and use $HOME instead. 

Or use it correctly, unquoted and unescaped.

Janis

> A literal '$HOME'
> won't work at all, but that's less likely to be a problem if your at all
> aware of how double quotes work in the shell.
> 
> I suggest that bash's undocumented behavior is less than helpful.
> I'll probably submit a bug report.
>