Re: What is the difference between $PWD and pwd?

[Eric Blake]

On 4/27/20 3:39 PM, Peng Yu wrote:
> Hi,
>
> Suppose that PWD is not manually set, I think $PWD and pwd should give
> the same results. If this is true, I don't understand why there are
> both $PWD and pwd. Does anybody know why both are defined?

They both exist, thanks to logical paths.  $PWD always tracks the 
shell's current logical path (which differs from the physical path if 
you changed directories through a symlink while using logical path 
tracking).  The pwd executable has two modes, logical (repeat the 
contents of $PWD, if it seems to be accurate) and physical (output a 
result that contains no symlinks).  Which mode is default (for both 'cd' 
and for 'pwd') is not specified by POSIX; bash defaults to logical mode, 
although some people detest the fact that under logical mode 'cd ..' and 
'ls ..' can end up acting on different directories and prefer to always 
use physical mode.  If you always use physical mode, then you are right 
that the two should never differ.

> Or they do not always give the same result? Thanks.

$ cd /tmp
$ mkdir a
$ ln -s a b
$ cd -L /tmp/b
$ echo $PWD
/tmp/b
$ pwd -L
/tmp/b
$ pwd -P
/tmp/a

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
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