This section provides a tutorial example, DirTree.pl, using a recursive method to read directories to print out a directory tree.
Both Unix and Windows systems organize file directories into a tree structure.
The following program. DirTree.pl, shows you how to traverse the directory tree,
and display directory entries:
#- DirTree.pl
#- Copyright (c) 1995 by Dr. Herong Yang, http://www.herongyang.com/
#
($dir) = @ARGV;
$dir = "." unless $dir;
&loopDir($dir, "");
exit;
sub loopDir {
local($dir, $margin) = @_;
chdir($dir) || die "Cannot chdir to $dir\n";
local(*DIR);
opendir(DIR, ".");
while ($f=readdir(DIR)) {
next if ($f eq "." || $f eq "..");
print "$margin$f\n";
if (-d $f) {
&loopDir($f,$margin." ");
}
}
closedir(DIR);
chdir("..");
}
Be careful, don't try this program in the root directory. It will produce
a very very long list of files and directories. I tried it on the working
directory where I stored my Perl notes and programs, and I got the following:
If you review DirTree.pl, you will see some interesting statements and techniques:
" $dir = "." unless $dir;" is used to assume a default directory, if nothing
specified on the command line.
" local($dir, $margin) = @_;" is used to make $dir and $margin as local variables.
This very important, since loopDir() is called recursively.
" local(*DIR);" is used to make DIR as local variable in any name spaces,
including directory handle name space. In fact, this is the only way to make
directory handle names local.
" if (-d $f) {" is used to test the directory entry to see if it is a
directory.
