Question

I have a pathname with placeholders in it which i want to substitute:

# an example path with a placeholder
my $path = '%myproject%Web/ui/images/';

# mapping of all placeholders   
my %placeholders = (
  myproject => 'myproject/installation/all'
);

# substituting all placeholders in the path
$path =~ s!%(.*?)%!/$placeholders{$1}/!g;

# works fine -> 'myproject/installation/all/Web/ui/images/'
print $path; 

This code works fine, but has one problem: I have a long list of filesnames and different placeholders specified (hence the hash). Now for the sake of more robustness I’d like to throw an error if there is a placeholder specified in the path which does not exist in the %placeholders mapping.

Is there a way to achieve that?

Answer 1

Now for the sake of more robustness I’d like to throw an error if there is a placeholder specified in the path which does not exist in the %placeholders mapping

This can be done very easily using /e:

$path =~ s{%([^%]+)%}{
   exists($path{$1})
      ? '/'.$path{$1}.'/'
      : die "Placeholder $1 does not exist"
}ge;

Note: I think it’s good to replace .*? with [^%]+ to prevent incorrect matching.