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Manipulating Files and Directories

Building on the previous File I/O section, we will now look at how we can modify various directory and file properties.

Manipulating Directories :: Directory Access

If you want to change directories you can issue the chdir command:

  chdir("/some/path") || die "Cannot chdir to /some/path ($!)";

In order to glob a list, you can do it in either of these two ways:
```
  @a = </some/path/*.c>
  @a = glob("/some/path/*.c");
```
This would create a list of all of the .c files in the /some/path directory. We could loop through a glob directly by:
```
  if (-d "/some/path") {
    $where = "/some/path";
  } else {
    $where = "/another/path";
  }
  while (defined($next = <$where/*.c>)) {
    print "found a c file in $where directory named $name\n";
  }
```
Notice we used the -d check for a directory for its existence. Very powerful indeed.

Manipulating Directories :: Directory Handles

Just like we can create file handles for our files, we can create directory handles for our directories!

Using Directory Handles:

  opendir(DIRHANDLE, "/some/path") || die "Cannot opendir /some/path: $!";
  foreach $name (sort readdir(DIRHANDLE)) {
    print "found file: $name\n";
  }
  closedir(DIRHANDLE);

This prints out a sorted directory listing. For an unsorted list, we could have simplified the loop construct:

  while ($name = readdir(DIRHANDLE)) {
    print "found file: $name\n";
  }

Remember to close your directory handles!

Manipulating Directories :: Creating and Removing Directories

There is no trick to creating and removing directories in Perl:
```
  mkdir("newdir", 0755) || die "Cannot mkdir newdir: $!";
  rmdir("olddir") || dir "Cannot rmdir olddir: $!";
```
Notice the 0755 in the mkdir function call is permission bits. A quick rundown: 4 = read, 5 = read + execute, 6 = read + write, 7 = read + write + execute. You need to set the execute bit on in order for you to access the directory.

Manipulating Files :: Removing and Renaming Files

Removing files can be done by using the unlink function:
```
  print "file to delete? ";
  chomp($name = <STDIN>);
  unlink($name) || die "Cannont unlink $name: $!";
```
You can even give unlink a glob or a list of files to delete.

Renaming files is a simple function call:

  rename("oldfilename.txt", "newfilename.txt") || die "Cannot rename file.txt: $!";
  rename("data.in", "/some/new/path/data.in") || die "Cannot rename data.in: $!";

Notice that Perl's rename function is almost the same as the mv command under *NIX.

Manipulating Files :: Linking

To create a symbolic link under Perl, use the symlink function:

  # Under *NIX shell:
  ln -s file.txt /some/other/path/reference.txt
  # Under Perl:
  symlink("file.txt", "/some/other/path/reference.txt") || die "Cannot symlink file.txt: $!";

Perl gives us a way to read symlinks:

  if (defined($x = readlink("reference.txt"))) {
    print "reference.txt points at '$x'\n";
  }

Manipulating Files :: Modifying Permissions

Modifying permissions is very similar to the shell chmod command:
```
  chmod(0644, "file1", "file2") || die "Cannot chmod file1, file2: $!";
```
Notice we can give a list of files to the chmod command (as we have seen with other File/Dir modification functions.

Manipulating Files and Directories Review

Perl proves again to be a swiss army knife of programming languages. We can modify our directories and files with ease, while ther Perl interpreter takes care of the gory details.