Thanks Chas., that's interesting! Here's my summary of what I've learnt from this:
1. The regex $foo =~ "\Asome string\Z" is equivalent to $bar = "\Asome string\Z"; # ends up as 'Asome stringB' with a warning $foo =~ /$bar/; i.e evaluate the string first and then stick it into the regex delimiters. 2. I'd never seen m?? before so if anyone else wants a good description and context for usage see http://perldoc.perl.org/perlop.html#Regexp-Quote-Like-Operators (search for ?PATTERN?) and http://perldoc.perl.org/functions/continue.html Andrew On Fri, Feb 24, 2017 at 1:50 PM, Chas. Owens <chas.ow...@gmail.com> wrote: > Be careful, it isn't actually a regex; it is a string that will be > compiled to a regex. You can see one difference here: > > #!/usr/bin/perl > > use v5.20; > use warnings; > > say "string matches:"; > for my $s ("foo", "AfooZ") { > say "\t$s: ", $s =~ "\Afoo\Z" ? "true" : "false"; > } > > say "regex matches:"; > for my $s ("foo", "AfooZ") { > say "\t$s: ", $s =~ /\Afoo\Z/ ? "true" : "false"; > } > > which outputs > > Unrecognized escape \A passed through at t.pl line 8. > Unrecognized escape \Z passed through at t.pl line 8. > string matches: > foo: false > AfooZ: true > regex matches: > foo: true > AfooZ: false > > To my knowledge, the only delimiters that do not require m or qr before > them are // and ??; however, they are not equivalent (and ?? must be m?? as > of Perl 5.22). The m?? operator only matches the first time it sees a > pattern and then will not match again until reset is called: > > #!/usr/bin/perl > > use v5.18; > use warnings; > > for ("fo", "foo", "fooo", "foooo") { > my ($match) = ?(fo+)?; > say $match // "no match"; > if (/fooo/) { > reset; > } > } > > Which outputs > > Use of ?PATTERN? without explicit operator is deprecated at t.pl line 7. > fo > no match > no match > foooo > > > On Thu, Feb 23, 2017 at 6:53 PM Andrew Solomon <and...@geekuni.com> wrote: > >> Thanks Uri! >> >> On Thu, Feb 23, 2017 at 10:32 PM, Uri Guttman <u...@stemsystems.com> >> wrote: >> >> On 02/23/2017 05:19 PM, Andrew Solomon wrote: >> >> Running Perl 18.2 I was surprised to discover that I can use single and >> double quotes as regex delimiters without the 'm' operator. >> >> For example, instead of writing >> >> "/usr/bin/perl" =~ m"/perl" >> >> I can just write >> >> "/usr/bin/perl" =~ "/perl" >> >> Can anyone point me to the documentation indicating which delimiters >> don't need the 'm' operator? >> >> >> you actually are thinking in the wrong direction. the =~ operator causes >> its right side to always be a regex unless the s/// or m// or tr/// ops are >> seen there. you can even use an expression or sub call or anything on the >> right of =~ and it will be parsed as a regex (if no op is there as i just >> said). >> >> you can easily check this out with something simple like "/usr/bin/perl" >> =~ "/pe" . "rl". >> >> so it isn't the delimiters as you think but the =~ op itself that makes >> it a regex. >> >> uri >> >> -- >> To unsubscribe, e-mail: beginners-unsubscr...@perl.org >> For additional commands, e-mail: beginners-h...@perl.org >> http://learn.perl.org/ >> >> >> >> >> >> -- >> Andrew Solomon >> >> Mentor@Geekuni http://geekuni.com/ >> http://www.linkedin.com/in/asolomon >> > -- Andrew Solomon Mentor@Geekuni http://geekuni.com/ http://www.linkedin.com/in/asolomon
