Environment Variables – What is $PWD vs Current Working Directory

environment-variablesterminology

So Wikipedia (link) tells me that the command pwd is short for "print working directory", and that makes sense.

But for the environment variable, the "P" has to be an acronym for something else than print.

I hear people talking about "current working directory", which sounds better and is more intuitive, but still the environment variable seems to be called $PWD, and not $CWD. Nobody ever says "Did you check the print working directory variable?".

I am currently playing around with the web application server uWSGI, and when running it tells me (on the uWSGI stats page):

"cwd":"/home/velle/greendrinks",

so they obviously like the (more intuitive acronym) cwd over pwd.

I guess I am trying to figure out if I misunderstood something, or if it is just a matter of having given the environment variable an unintuitive name?

Best Answer

That depends on what you're doing.  First of all, $PWD is an environment variable and pwd is a shell builtin or an actual binary:

$ type -a pwd
pwd is a shell builtin
pwd is /bin/pwd

Now, the bash builtin will simply print the current value of $PWD unless you use the -P flag.  As explained in help pwd:

pwd: pwd [-LP]

    Print the name of the current working directory.

    Options:

      -L
          print the value of $PWD if it names the current working directory
      -P
          print the physical directory, without any symbolic links

    By default, ‘pwd’ behaves as if ‘-L’ were specified.

The pwd binary, on the other hand, gets the current directory through the getcwd(3) system call which returns the same value as readlink -f /proc/self/cwd.  To illustrate, try moving into a directory that is a link to another one:

$ ls -l
total 4
drwxr-xr-x 2 terdon terdon 4096 Jun  4 11:22 foo
lrwxrwxrwx 1 terdon terdon    4 Jun  4 11:22 linktofoo -> foo/
$ cd linktofoo
$ echo $PWD
/home/terdon/foo/linktofoo
$ pwd
/home/terdon/foo/linktofoo
$ /bin/pwd
/home/terdon/foo/foo

So, in conclusion, on GNU systems (such as Ubuntu), pwd and echo $PWD are equivalent unless you use the -P option, but /bin/pwd is different and behaves like pwd -P.

Source https://askubuntu.com/a/476633/291937

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