The files we created in the previous chapter were generally in the same place as our program. But modern operating systems let us organize files into directories, allowing us to keep our Beatles MP3s away from our important Llama book chapter sources so that we don’t accidentally send an MP3 file to the publisher. Perl lets you manipulate these directories directly, in ways that are even fairly portable from one operating system to another.
Your program runs with a “working directory,” which is the
starting point for relative pathnames. That is, if you refer to the file
fred, that means
fred in the current working directory.
chdir operator changes
the working directory. It’s just like the Unix shell’s cd command:
chdir "/etc" or die "cannot chdir to /etc: $!";
Because this is a system request, the value of
$! will be set if an error occurs. You should
$! when a false value
is returned from
chdir, since that
indicates that something has not gone as requested.
The working directory is inherited by all processes that Perl starts (we’ll talk more about that in Chapter 16). However, the change in working directory cannot affect the process that invoked Perl, such as the shell. So you can’t make a Perl program to replace your shell’s cd command.
If you omit the parameter, Perl determines your home directory as best as it can and attempts to set the working directory to your home directory, similar to using ...