How do I build Perl regular expressions dynamically?

Question

I have a Perl script that traverses a directory hierarchy using File::Next::files. It will only return to the script files that end in \".avi\", \".flv\", \".mp3\", \".mp4\", a

Answer 1

Assuming that you've parsed the configuration file to get a list of extensions and ignored directories, you can build the regular expression as a string and then use the qr operator to compile it into a regular expression:

my @extensions = qw(avi flv mp3 mp4 wmv);  # parsed from file
my $pattern    = '\.(' . join('|', @wanted) . ')$';
my $regex      = qr/$pattern/;

if ($file =~ $regex) {
    # do something
}

The compilation isn't strictly necessary; you can use the string pattern directly:

if ($file =~ /$pattern/) {
    # do something
}

Directories are a little harder because you have two different situations: full names and suffixes. Your configuration file will have to use different keys to make it clear which is which. e.g. "dir_name" and "dir_suffix." For full names I'd just build a hash:

%ignore = ('.svn' => 1);

Suffixed directories can be done the same way as file extensions:

my $dir_pattern = '(?:' . join('|', map {quotemeta} @dir_suffix), ')$';
my $dir_regex   = qr/$dir_pattern/;

You could even build the patterns into anonymous subroutines to avoid referencing global variables:

my $file_filter    = sub { $_ =~ $regex };
my $descend_filter = sub {
    ! $ignore{$File::Next::dir} &&
    ! $File::Next::dir =~ $dir_regex;
};

my $iter = File::Next::files({
    file_filter    => $file_filter,
    descend_filter => $descend_filter,
}, $directory);