Re: regex puzzle
Roberto Ruiz wrote:
On Fri, Jul 29, 2005 at 01:48:15PM +0800, bingfeng zhao wrote:
See following sample code:
my @address = ("http://test";, "http://";, "www", "", "ftp:/foo" );
for (@address)
{
print "\"$_\" passed! \n" if /^((http|ftp):\/\/)?.+$/;
# ^ ^
# these parentesis are making an atom of the
# enclosed part of the regex
}
why "http://"; and "ftp:/foo" can pass the check?
Because the () atomize the first part of your regex and then the ? is
asking for 0 or 1 of that atom.
Droping the ()?: /^(http|ftp):\/\/.+$/
Or, more redable: m!^(http|ftp)://.+$!
And a little shorter: m!^(ht|f)tp://.+$!
HTH,
Roberto Ruiz
Nice shot!!
And yes, the ? is the culprit.
Wouldn't is be simpler if you just replaced .+$ with \w+ to make sure
that there was something that matched. Who cares if you match something
to the end of the line? You also are accepting strings like:
http://`rm -rf /.`
m|(ht|f)tp://\w+|
Because you really would be expecting something similar to 'www' to follow?
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Re: regex puzzle
/^((http|ftp):\/\/)?.+$/
In my opinion the problem is that ' .+' means 'anything',
and ''" is matched by this part of the regex
("" is anything too).
regards
Pedro
- Original Message -
From: "Roberto Ruiz" <[EMAIL PROTECTED]>
To:
Sent: Friday, July 29, 2005 6:52 AM
Subject: Re: regex puzzle
On Fri, Jul 29, 2005 at 01:48:15PM +0800, bingfeng zhao wrote:
See following sample code:
my @address = ("http://test";, "http://";, "www", "", "ftp:/foo" );
for (@address)
{
print "\"$_\" passed! \n" if /^((http|ftp):\/\/)?.+$/;
# ^ ^
# these parentesis are making an atom of the
# enclosed part of the regex
}
why "http://"; and "ftp:/foo" can pass the check?
Because the () atomize the first part of your regex and then the ? is
asking for 0 or 1 of that atom.
Droping the ()?: /^(http|ftp):\/\/.+$/
Or, more redable: m!^(http|ftp)://.+$!
And a little shorter: m!^(ht|f)tp://.+$!
HTH,
Roberto Ruiz
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Re: regex puzzle
On Fri, Jul 29, 2005 at 01:48:15PM +0800, bingfeng zhao wrote:
> See following sample code:
>
> my @address = ("http://test";, "http://";, "www", "", "ftp:/foo" );
>
> for (@address)
> {
> print "\"$_\" passed! \n" if /^((http|ftp):\/\/)?.+$/;
# ^ ^
# these parentesis are making an atom of the
# enclosed part of the regex
> }
> why "http://"; and "ftp:/foo" can pass the check?
Because the () atomize the first part of your regex and then the ? is
asking for 0 or 1 of that atom.
Droping the ()?: /^(http|ftp):\/\/.+$/
Or, more redable: m!^(http|ftp)://.+$!
And a little shorter: m!^(ht|f)tp://.+$!
HTH,
Roberto Ruiz
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Re: regex puzzle
bingfeng zhao wrote:
See following sample code:
use warnings;
use strict;
my @address = ("http://test";, "http://";, "www", "", "ftp:/foo" );
for (@address)
{
print "\"$_\" passed! \n" if /^((http|ftp):\/\/)?.+$/;
}
the running result is:
"http://test"; is valid.
"http://"; is valid.
"www" is valid.
"ftp:/foo" is valid.
why "http://"; and "ftp:/foo" can pass the check?
Because ((http|ftp):\/\/) is optional ( the ? following it does that ),
so any line with anything between the start and end of the line will pass.
--
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a.k.a Greven, TuxPower Belief without evidence in what is told
<[EMAIL PROTECTED]> by one who speaks without knowledge,
4112.38 BogoMIPS of things without parallel.
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RE: regex puzzle
Oh， bug，it should be
use warnings;
use strict;
my @address = ("http://test";, "http://";, "www", "", "ftp:/foo" );
for (@address)
{
print "\"$_\" is valid. \n" if /^((http|ftp):\/\/)?.+$/;
}
|-Original Message-
|From: bingfeng zhao [mailto:[EMAIL PROTECTED]
|Sent: Friday, July 29, 2005 1:48 PM
|To: Perl Beginners List
|Subject: regex puzzle
|
|See following sample code:
|
|
|use warnings;
|use strict;
|
|my @address = ("http://test";, "http://";, "www", "", "ftp:/foo" );
|
|for (@address)
|{
|print "\"$_\" passed! \n" if /^((http|ftp):\/\/)?.+$/; }
|
|the running result is:
|"http://test"; is valid.
|"http://"; is valid.
|"www" is valid.
|"ftp:/foo" is valid.
|
|why "http://"; and "ftp:/foo" can pass the check?
|
|
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