Two simple steps:

• 1. Read the contents of each directory into two separate arrays. See readdir
• 2. Read How can I find the union/difference/intersection of two arrays?.

update: There are quite a few nodes on PerlMonks about comparing arrays. Do use the search.

opendir, readdir and closedir---how did I never know about those? I currently do quite a lot of reading in the contents of directories, and so far I've always done it by endless constructs like

$dir_list=`ls -1 */*`;
@files=split(/\n/,$dir_list);
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D'oh! and thanks! why_bird
........
Those are my principles. If you don't like them I have others.
-- Groucho Marx
.......

Also, if your SysAdmin won't let you install Perl modules in the usual place (/usr/lib* usually I think), but you can install elsewhere, this works for me (I tried to find the reference on Google, but couldn't):

• download, and unzip the file for MyModule from CPAN
• Extract to directory ~/MyDir
• cd to ~/MyDir/MyModule
• type perl Makefile.PL PREFIX="~/PerlModules/"
• type make test; make; make install as usual for a manual install
• Find the directory in ~/PerlModules in which MyModule.pm resides.
• Edit your ~/.cshrc (different for different shells) to contain the line 'setenv PERL5LIB
~/PerlModules/Directory_For_MyModule'

edit: Found it! Here is a reference about how to install without root permissions, which also tells you an alternative to setting the environment variable PERL5LIB. And it talks about what to do on Windows.

$ mkdir -p dir1/a/b/c
$ mkdir -p dir2/a/b
$ echo 1a1 > dir1/a/1
$ echo 2a1 > dir2/a/1
$ touch dir1/a/2
$ touch dir2/a/2
$ touch dir1/a/b/x
$ diff -rq dir1 dir2
Files dir1/a/1 and dir2/a/1 differ
Only in dir1/a/b: c
Only in dir1/a/b: x
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