Current working directory in Perl (cwd, pwd)
Every process and every application running on your computer is associated with a directory on the filesystem, called the "current working directory".
On Microsoft Windows, if you open a Command Shell (by running cmd) you'll see the current working directory of this shell in the prompt. (e.g. c:\users\Foo Bar\Desktop> indicates that the working directory of this cmd window is c:\users\Foo Bar\Desktop>. When configuring a new launcher icon, one can set what should be the initial working directory of the process.
On Linux, Apple OSX, and Unix in general the command pwd means print working directory and it is used to fetch the current working directory.
Perl has a standard module called Cwd that provides this functionality via a number of functions.
use Cwd qw(cwd); my $dir = cwd; print "$dir\n";
use Cwd qw(getcwd); my $dir = getcwd; print "$dir\n";
cwd or getcwd?
In most cases cwd and getcwd will return the same path, but there can be differences. Specifically if symbolic links are involved.
Let's say we create a directory called "abc" and a symbolic link pointing to that directory:
$ mkdir abc $ ln -s abc def $ ls -l drwxr-xr-x 2 gabor staff 68 Aug 9 09:29 abc lrwxr-xr-x 1 gabor staff 3 Aug 9 09:30 def -> abc
The resulting directory structure looks like this:
dir/ abc def -> abc
Now let's see what do cwd and getcwd return if we are in either of those directories.
use 5.010; use strict; use warnings; use Cwd qw(cwd getcwd); say cwd; say getcwd;
$ cd abc $ perl ../cwd.pl /dir/abc /dir/abc
$ cd ../def $ perl ../cwd.pl /dir/def /dir/abc
In other words cwd will return the symbolic link (the logical path to where we are) while getcwd will resolve the symbolic link and return the real directory (the hard link) of where we are.
Published on 2017-03-18