regexp "?" delimiter

cmic has asked for the wisdom of the Perl Monks concerning the following question:

The following code (using Perl 5.24 on Debian) yields this error:
syntax error at ./regexp.pl line xx, near "if ?"

my ($DICT, $first, $last);
open $DICT, "<", "/usr/share/dict/words";
while (<$DICT>) {
#FIXME
    $first = $1 if ?(^neuro.*)?;  #  <- syntax error here 
    $last = $1 if  /(^neuro.*)/;
}
close $DICT;
print "first : $first, last : $last \n";
print "-" x 10, "\n";
#
[download]

Is it a deprecated usage of the "?" delimiter ?
Or what ?

-- cmic. Life helps. Perl Too.

Comment on regexp "?" delimiter Download Code

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Re: regexp "?" delimiter by choroba (Cardinal) on Jun 11, 2019 at 14:04 UTC
Please, edit your node and move the question up away from the signature part. Some monks have turned signature display off. The `?...?` delimiter should be written `m?...?` starting with 5.22. I'd extend the original code with `use Syntax::Construct qw{ ?? };` [download] if it were still running in the original environment. But adding the `m` would work in the old versions, too, so it's an unnecessary step. `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l] [select]
Re: regexp "?" delimiter by Corion (Patriarch) on Jun 11, 2019 at 14:05 UTC
The support for `?PATTERN?` matching was removed in Perl 5.22.0, four years ago. ~~You will need to use a matching operator and operand, like `$_ =~ ?(^neuro.*)?`~~. You will need to use a prefixed `m`, as choroba and Eily show. In the perldelta, you can read what changed between each version of Perl 5.	[reply] [d/l] [select]
Re: regexp "?" delimiter by Eily (Monsignor) on Jun 11, 2019 at 14:03 UTC
To use a character as a delimiter, you have to prepend the corresponding operator to indicate what it is the delimiter of, q for a single quote string, y for a transliteration, m for a matching operation (regex)... The trick is, when perl sees / in a place where it could expect a regex, is guesses that you meant m/. So `/(^neuro.)/` is actually `m/(^neuro.)/` where m means "make / the delimiter for a match operation". So you should use `m?(^neuro.*)?` Edit: oh I thought the m had always been required except for //, turns out there used to be an exception for ?? as well.	[reply] [d/l] [select]
Re: regexp "?" delimiter by cmic (Acolyte) on Jun 12, 2019 at 13:14 UTC
Thanks Eily for clear explanations. -- cmic. Retired Sysadmin....	[reply]