From CPAN doc

find

   find(\&wanted,  @directories);
      find(\%options, @directories);
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find() does a depth-first search over the given @directories in the order they are given. For each file or directory found, it calls the &wanted subroutine.Additionally, for each directory found, it will chdir() into that directory and continue the search, invoking the &wanted function on each file or subdirectory in the directory.

You can do this way.

my $file='foo';        
my directory='a';                                                     
+                              
sub check_existance {                                                 
+                             
    if ( -e $_ && $_ eq $file ) {                                     
+                                 
        print "Found file '$_' in directory '$File::Find::dir'\n";    
+                                 
    }                                                                 
+                                 
}       

find( \&check_existance, $directory );
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The check_existance function takes no arguments but rather does its work through a collection of variables.

$File::Find::dir is the current directory name,

$_ is the current filename within that directory

$File::Find::name is the complete pathname to the file.

The above variables have all been localized and may be changed without affecting data outside of the check_existance function.