How to use Perl's grep to find a particular file by matching a pattern in its name

Question

I have a string stored in a Perl variable that should match with the beginning part of a file name stored in a directory.

I use this variable to find the file matching this pattern from the directory, using Perl's grep. Here's what I am doing:

    opendir (DIR, "data/testroot/") or die "$!";
    @file1 = <$f1/*.hdf>
    foreach(@file1){
       $patt = substr(basename($_),0,$ind);
       $file2 = grep {/${patt}*\.hdf/} readdir(DIR);
       #other code follows.......
    }
    closedir(DIR);

First, I get a list of all files in folder f1 and storing them in the array @file . Then for each entry in @file1 , I extract the first few characters, store them in $patt , then try to pick up similar files from another folder data/testroot/ which have the matching beginning pattern as stored in $patt .

That grep $file2 = grep {/${patt}*\\.hdf/} readdir(DIR); is not working.

Answer 1

I think you want to find all *.hdf files in directory A whose filenames match the first $ind characters of any such file in directory B?

You should use either glob or readdir for both directories, but not both. In this case glob seems to be the best bet as it allows you to select all *.hdf files from A without having to check them with the regex.

The program below seems to do what you need. I have substituted sample values for $f1 and $ind .

use strict;
use warnings;

use File::Basename;

my $f1 = 'data';
my $f1 = 'data/testroot';
my $ind = 6;

foreach (glob "$f1/*.hdf") {
  my $patt = substr(basename($_), 0, $ind);
  my @match = glob "$f2/$patt*.hdf";

  #other code follows.......
}

Answer 2

${patt}*\\.hdf means "0 or more occurrences of $patt, followed by .hdf". Are you sure you don't mean "$patt, followed by arbitrary text, followed by .hdf"?

That would be /${patt}.*\\.hdf/ .