http://qs321.pair.com?node_id=281907

AcidHawk has asked for the wisdom of the Perl Monks concerning the following question:

Hi,

I am wanting to search for file names that conform to a certain pattern. I want to read the pattern from a config file, something like aaaa-nnnnnnnn. The config part is not the problem, the template bit is. This config value should match files that have 4 alpha characters, then a -, then 8 numeric characters.

I have looked (a bit) for template modules but the majority of these are for HTML.

Some pseudo code to try and help explain. 

*** Get aaaa-nnnnnnnn from config file *** I am using XML::Simple

while ($file = readdir DIR) {
    next if $file =~/^\./ || $file not matched by $filename_template;
    
    *** Carry on to do something with a file that does conform...

[download]
The files I want to do something with look something like ABCD-13022003*.* or even ZZZZ-99999999*.* I would also like to be able to change the config to something like aa-nn-aa, which would match XX-55-DD*.* files.

Has anyone any direction to point me in?

-----
Of all the things I've lost in my life, its my mind I miss the most.

Replies are listed 'Best First'.
Re: Filename Template
by Abstraction (Friar) on Aug 07, 2003 at 14:48 UTC
[reply]
      Further to that ... 
      use File::Find::Rule;

my $template = 'aaaa-nnnnnnnn';
(my $regex = $template)
  =~ s/([an])/$1 eq 'a' ? '[a-z]' : '[0-9]'/eig;

my $matcher = rule(
  file     =>
  maxdepth => 1,
  name     => qr/^$regex/i,
  start    => $ARGV[0]
);

while(my $file = $matcher->match) {
  ...
}

      [download]
      See. the File::Find::Rule docs for more info.
      HTH

      _________
      broquaint

[reply]
[d/l]
      Abstraction,
      To expound on what you have said: 
      #!/usr/bin/perl -w
use strict;
use File::Find::Rule;

my @files = File::Find::Rule->file()
                            ->name( qr/^[a-zA-Z]{4}-\d{8}/ )
                            ->in( / );

      [download]
      It appeared at first in the docs that all you could do was file globs, but later on I saw a regex, so I think this will work.

      Cheers - L~R

      Update: Bah, broquaint beat me to it, so yes it will work. What's worse - his solution provides the ability to modify the template without modifying the regex. I guess the only thing I would have done differently is changed the character class to [a-zA-Z] instead of using /i for speed reasons - but if it runs a tad bit slower it just means you can go get more caffeine.

[reply]
[d/l]
[select]

        even a simple readdir should do the trick

        #!/usr/bin/perl -w

use strict;

my $dir     = '/some/dir';
my $file_re = qr/^(?:\.+|[a-zA-Z]{4}-[0-9]{8})$/;

opendir(DIR, $dir) or die "opening $dir: $!\n";

for ( grep(!/$file_re/, readdir(DIR)) ) {
# deal with non conforming file names here
}
closedir(DIR);

        [download]

        use perl;

[reply]
[d/l]
Re: Filename Template
by larsen (Parson) on Aug 07, 2003 at 14:50 UTC
    ... the template bit is. This config value should match files that have 4 alpha characters, then a -, then 8 numeric characters. ...
    If you say regular expression instead of template maybe you'll find the light.
[reply]
      To expand on this, general usage of the following terms could be defined as follows:
      • Template: A format used for describing output
      • Format: A way of abstractly expressing how something should look, as opposed to what the content should be
      • Regular Expression: A way of defining some set of matching criteria, often used for limiting or parsing input
      • Mask: A format used for constraining input
      Hopefully, that helps!

      ------
      We are the carpenters and bricklayers of the Information Age.

      The idea is a little like C++ templates, except not quite so brain-meltingly complicated. -- TheDamian, Exegesis 6

      Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.

[reply]
        Yes. And it offers me a way to expand my previous answer. You say that a template is "a format used for describing output". I'll go further, saying that a template generates a language (i.e. a set of strings). On the other hand a regular expression denotes a language, then is usable to recognize strings that belong or not to a set. Since the original question asked for a way to recognize strings in a set, I suggested to change terminology in order to be conducted to the right abstraction that Perl provides.
[reply]

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