Find a file in a list of directories

[grinder]

This snippet searches a series of directories for a file. For instance, you may want to open the file 'foo.txt', but it could be in any one of a number of directories, so you want to search them one after the other until you find it.

An analogy would be the way a shell finds a program based on the value of the PATH environment variable.

asdfgroup's remarks noted.

    my $target = 'foo.txt';
    my $file = do {
        my $target = undef;
        foreach my $dir( qw{ /tmp /var/tmp /foo /bar } ) {
            my $t = "$dir/$target";
            # nb: you might want to use -e here
            # but -f might be what you *really* want, YMMV
            if( -f $t ) {
                $target = $t;
                last;
            }
        }
        $target;
    };

    if( $target ) {
        open IN, $target or die "Cannot open $target for input: $\n";
        # ...
    }
    else {
        die "Can't find $target.\n";
    }

[asdfgroup]

more compact version of your code. And you should use '-e' test instead of '-t'

#!/usr/bin/perl
sub FileFinder {
   my ($target, @dir) = @_;
   return (grep {-e $_} map {"$_/$target"} @dir)[0];
}
 
open(F, FileFinder('FileFinder.pl', qw(some/ dirs/ ./)) || die "File n
+ot found") or die $!;

[demerphq]

IMO in general grep and map shouldn't be chained together, map can do greps job without having retraverse the array.

return (map{-e "$_/$target" ? "$_/$target" : ()} @dir)[0];

And frankly why bother with map and grep at all? This is much more efficient.

sub FileFinder {
  my $target=shift;
  -e "$_/$target" && return "$_/$target" foreach @_;
  undef 
}

Oh and before the premature optimization police arrest me, remember that we are searching a filesystem (possible remote etc) here. That call to -e could take a while and if we have to do more of them than we really need to then we could end up wasting a lot of time.

Adjust the file test to your taste ;-)

Yves / DeMerphq
---
Writing a good benchmark isnt as easy as it might look.