To print current/present working directory environment variable $PWD and command pwd are available. So, What is difference in usage of both? or What should be chose for specific purpose?
2 Answers
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.
Both will return the same result if you use them without options for all working directories, including when in symbolic links.
However, from man pwd:
-P, --physical avoid all symlinks This would mean executing pwd -P when in symbolic links which point to some other directories will print the path to the original directory.
As an example, if you have a symbolic link /var/run that points to /run and you are currently in /var/run/ directory, executing
echo $PWD will return:
/var/run and will be the same for pwd. However, if you execute:
pwd -P will return
/run Thus, it depends which path you require: the actual path without symbolic links or the present directory ignoring the symbolic links. The only difference between between pwd -P and echo $PWD is when there are symbolic links.
