Learning Perl on Win32 Systems

Modifying Permissions

The permissions on a file or directory define who (in broad categories) can do what (more or less) to that file or directory. Under UNIX, the typical way to change permissions on a file is with the chmod command. As a Windows user, you may be more used to the attrib command. Perl changes permissions with the chmod function. This operator takes an octal numeric mode and a list of filenames, and attempts to alter the permissions of all the filenames to the indicated mode. To make the files fred and barney with both read/write attributes, for example, do something like this:

chmod(0666,"fred","barney");

In short, the UNIX (and Perl) concept of file permissions consists of a bit for read, write, and execute rights for the user, the user’s group, and everyone else. These bits are combined to create the mode. Because Win32 systems have a significantly different concept of permissions, you don’t need to worry about all of the different possible values for the mode. Table 13.1 presents a couple of key values.

Table 13-1. Key Values for File Permissions

Mode	Meaning
0666	Read/Write
0444	Read only

Win32 systems determine whether or not a file is executable based on the file extension, so we’re not going to worry about the execute bits. Furthermore, even though some Windows NT filesystems support advanced user/group rights, the current Perl implementation doesn’t support access to these rights via chmod.

The return value of chmod is the number of files successfully ...