Hi fellow monks, I'm looking for a solution to join together all the second-level keys from a hash constructed like that : 
%replaces = 
{ "foo"
   => ( 'W100' => 'W102',
        'W101' => 'W103',
		...),
"bar"
   => ( 'W120' => 'W99',
        'W121' => 'W104',
		...),
... }
For instance, the hash shown below should led to the string W100|W101|W120|W121. Would it be possible to find a one-liner expression, or at least, a graceful piece of code to perform this ? I tried this : 
my $expr = join '|', keys(%{$replaces{$_}}) foreach keys(%replaces);
But $expr remains undefined after this line. I ended up hardcoding the expecting first-level values for the current run, but it's a dirty solution : 
my $expr = join '|', (keys(%{$replaces{'foo'}}), keys(%{$replaces{'bar'}}));
Thanks for any help on that !

In reply to One-liner to join keys on a two-dimensionnal hash ? by Anonymous Monk

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