Re^2: compare lists and delete unwanted from file

Thankyou for your help. I have been trying to get a handle on hash references so this will be good. However, I don't understand the code snippet below. Specifically, what is the "(?" and the //gw.

my $geneids_to_remove = {}; # create a hash reference
$text =~ s/(\w+)
  (?{ # in regex code
    $geneids_to_remove->{$1} = 1; # store geneids in a hash
  })
//gx;
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Can you also explain the part below in more detail. Specifically, what does the /x do?

my $rx_find_geneid = qr/^(\w+) (?{ $gene_id = $1; })/x;
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Re^3: compare lists and delete unwanted from file by muppetjones (Novice) on Mar 14, 2012 at 17:28 UTC
Of course! The (?{ ... }) is how you insert code into a regex. Whenever you see (? ... ), it generally means you are doing something with whatever is found inside, but you don't want to capture it. For instance (?: ... ) works just like a capture group but without actually capturing. Whenever you insert code into a regex, it's always a good idea to add the /x modifier, which tells the regex compiler to ignore all whitespace. This means you'll either need to escape whitespace (i.e., '\ '), or (even better) just use \s. The /g modifier means to match globally. This does different things depending on whether you're using s/// or m//. The former does it all at once, but the latter simply continues matching wherever the previous match left off, meaning you need a loop to match everything.	[reply]

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Re^3: compare lists and delete unwanted from file
by muppetjones (Novice) on Mar 14, 2012 at 17:28 UTC

Of course!

The (?{ ... }) is how you insert code into a regex. Whenever you see (? ... ), it generally means you are doing something with whatever is found inside, but you don't want to capture it. For instance (?: ... ) works just like a capture group but without actually capturing.

Whenever you insert code into a regex, it's always a good idea to add the /x modifier, which tells the regex compiler to ignore all whitespace. This means you'll either need to escape whitespace (i.e., '\ '), or (even better) just use \s.

The /g modifier means to match globally. This does different things depending on whether you're using s/// or m//. The former does it all at once, but the latter simply continues matching wherever the previous match left off, meaning you need a loop to match everything.

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