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Date: Thu, 23 May 2024 06:59:42 -0700
From: Collin Funk <>
To: Leah Neukirchen <>, Rich Felker <>
Subject: Re: getusershell should ignore comments and empty lines.

Hi Rich and Leah,

On 5/23/24 6:45 AM, Leah Neukirchen wrote:
>>     "A hash mark (``#'') indicates the beginning of a comment;
>>     subsequent characters up to the end of the line are not
>>     interpreted by the routines which search the file."
>> This isn't very clear whether # is only a comment on the beginning of
>> a line (after potential whitespace?) or whether # appearing in a line
>> with a shell pathname is a comment or part of the pathname. If it's a
>> comment, it's not clear if whitespace before it is part of the shell
>> pathname -- e.g. does "/bin/sh # best shell" define "/bin/sh" or
>> "/bin/sh " as the shell pathname?
>> It sounds like nobody ever thought about whitespace, quoting, or
>> rigorous comment syntax here...
> True:
> OpenBSD drops the rest of the line with "#" and ignores lines not
> starting with a "/".
> glibc drops the rest of the line with "#", elides spaces after the
> entry, and skips everything before the first "/" (quite bold).

I noticed the glibc behavior as well, but I thought the BSDs did it
too. Like this:

     'bin/bash' -> '/bash'

which is interesting. :)

I think the general algorithm is read a single line. Find the first
'/' character and then begin at the next character. Then continue
until the end of line or other whitespace character. Perhaps the
others felt that was awkward and changed it, I am not sure.

I think it would be nice to ignore lines starting with '#' though and
empty lines. That should cover 99% of cases. Most distributions,
including Alpine Linux, come with an '/etc/shells' like this:

# Some commentary redirecting to a man page or other documentation.


I doubt anyone changes it from that simple format.


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