_learning perl_, ch12, 7.I.2002, nh

DIRECTORY ACCESS

changing directories in perl uses the 'chdir' command
                                       ^^^^^
                                       takes one argument
-------------------------------------------------------                                    
|  chdir ("/etc") || die "cannot cd to /etc ($!)\n";  |
---~~~~~-----------------------------------------------                                    

    "every process has its own current directory.  when a new process
    is launched, it inherits its parent's current directory, but
    that's the end of the connection.  if your perl program changes
    its director, it won't affect the parent shell that launched the
    perl process.  likewise, the processes that the perl program
    creates cannot affect that perl program's current direectory.
    the current directory for these new processes are inherited from
    the perl program's current directory."   - p. 130

globbing
~~~~~~~~
  returns the same that an echo command with the same parameters
  would:
  
  @a = </etc/host*>;        # @a gets all files that begin with 'host'
  @a = glob("/etc/host*");  # in the /etc directory
    |
    `-> either one works fine
        multiple arguments permitted:
          @a = <a* b*>;

  if you want to interpolate a variable *by itself*, do it like:
      <${var}> 
  -- otherswise it'd be a filehandle!!

directory handles
~~~~~~~~~~~~~~~~~
  * use all UPPERCASE
  * use the directory handle to read a list of files w/in the
    directory
  * always read-only

opening & closing directories
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    opendir(ETC,"/etc") || die "cannot opendir /etc: $!\n";
    closedir(ETC);    # automatically closed before they're reopened
                      # or at the end of the program

reading a directory handle
~~~~~~~~~~~~~~~~~~~~~~~~~~
  read list of names with readdir
                          ^^^^^^^
                          takes one parameter - the direcotry handle
                          
  * each invocation returns the next filename (just the basename, not
    the complete path)
  * if no more names, returns "undef"

  opendir(ETC,"/etc") || die "no etc?: $!\n";
  while ($name = readdir(ETC)) {
    print $name\n";
  }
  closedir(ETC);
      
  ***sorted list of names***

  opendir(ETC,"/etc") || die "no etc?: $!\n";
  foreach $name (sort readdir(ETC)) {
    print "$name\n";
  }
  closedir(ETC);