Say I have strings like these:
bunch of other html<a href="http://domain.com/133742/The_Token_I_Want.zip" more html and stuff
bunch of other html<a href="http://domain.com/12345/another_token.zip" more html and stuff
bunch of other html<a href="http://domain.com/0981723/YET_ANOTHER_TOKEN.zip" more html and stuff
What is the regular expression to match The_Token_I_Want, another_token, YET_ANOTHER_TOKEN?
Appendix B of RFC 2396 gives a doozy of a regular expression for splitting a URI into its components, and we can adapt it for your case
^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*/([^.]+)[^?#]*)(\?([^#]*))?(#(.*))?
#######
This leaves The_Token_I_Want in $6, which is the “hashderlined” subexpression above. (Note that the hashes are not part of the pattern.) See it live:
#! /usr/bin/perl
$_ = "http://domain.com/133742/The_Token_I_Want.zip";
if (m!^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*/([^.]+)[^?#]*)(\?([^#]*))?(#(.*))?!) {
print "$6\n";
}
else {
print "no match\n";
}
Output:
$ ./prog.pl
The_Token_I_Want
UPDATE: I see in a comment that you're using boost::regex, so remember to escape the backslash in your C++ program.
#include <boost/foreach.hpp>
#include <boost/regex.hpp>
#include <iostream>
#include <string>
int main()
{
boost::regex token("^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*"
"/([^.]+)"
// ####### I CAN HAZ HASHDERLINE PLZ
"[^?#]*)(\\?([^#]*))?(#(.*))?");
const char * const urls[] = {
"http://domain.com/133742/The_Token_I_Want.zip",
"http://domain.com/12345/another_token.zip",
"http://domain.com/0981723/YET_ANOTHER_TOKEN.zip",
};
BOOST_FOREACH(const char *url, urls) {
std::cout << url << ":\n";
std::string t;
boost::cmatch m;
if (boost::regex_match(url, m, token))
t = m[6];
else
t = "<no match>";
std::cout << " - " << m[6] << '\n';
}
return 0;
}
Output:
http://domain.com/133742/The_Token_I_Want.zip:
- The_Token_I_Want
http://domain.com/12345/another_token.zip:
- another_token
http://domain.com/0981723/YET_ANOTHER_TOKEN.zip:
- YET_ANOTHER_TOKEN
/a href="http://domain.com/[0-9]+/([a-zA-Z_]+).zip"/
Might want to add more characters to [a-zA-Z_]+
You can use:
(http|ftp)+://[[:alnum:]./_]+/([[:alnum:]._-]+).[[:alnum:]_-]+
([[:alnum:]._-]+) is a group for the matched pattern, and in your example its value will be The_Token_I_Want. to access this group, use \2 or $2, because (http|ftp) is the first group and ([[:alnum:]._-]+) is the second group of the matched pattern.
Try this:
/(?:f|ht)tps?:/{2}(?:www.)?domain[^/]+.([^/]+).([^/]+)/i
or
/\w{3,5}:/{2}(?:w{3}.)?domain[^/]+.([^/]+).([^/]+)/i
First, use an HTML parser and get a DOM. Then get the anchor elements and loop over them looking for the hrefs. Don't try to grab the token straight out of a string.
Then:
The glib answer would be:
/(The_Token_I_Want.zip)/
You might want to be a little more precise then a single example.
I'm guessing you are actually looking for:
/([^/]+)$/
m/The_Token_I_Want/
You'll have to be more specific about what kind of token it is. A number? A string? Does it repeat? Does it have a form or pattern to it?
It's probably best to use something smarter than a RegEx. For example, if you're using C# you could use the System.Uri class to parse it for you.
Related
Whenever I use a regex function it matches the entire string for some reason.
#include <iostream>
#include <regex>
int main() {
std::string text = "This (is a) test";
std::regex pattern("\(.+\)");
std::cout << std::regex_replace(text, pattern, "isnt") << std::endl;
return 0;
}
Output: isnt
Your pattern unfortunately is not what it seems to be. Here is the problem.
Imagine for some reason you want to match tabs in with you regex. You might try this.
std::regex my_regex("\t");
This would work, but the string your std::regex class has seen is " ", not "\t". This is because of how C++ threats escaped characters. To pass literal "\t", you had to do the following.
std::regex my_regex("\\t");
So the correct syntax for your regex is.
std::regex pattern("\\(.+\\)");
I'm trying to write a regular expression in C++ to match a base64 encoded string. I'm quite familiar with writing complex regular expressions in Perl so I started with that:
use strict;
use warnings;
my $base64_regex = qr{
(?(DEFINE)
(?<B64>[A-Za-z0-9+/])
(?<B16>[AEIMQUYcgkosw048])
(?<B04>[AQgw])
)
^(
((?&B64){4})*
(
(?&B64){4}|
(?&B64){2}(?&B16)=|
(?&B64)(?&B04)={2}
)
)?$}x;
# "Hello World!" base64 encoded
my $base64 = "SGVsbG8gV29ybGQh";
if ($base64 =~ $base64_regex)
{
print "Match!\n";
}
else
{
print "No match!\n"
}
Output:
Match!
I then tried to implement a similar regular expression in C++:
#include <iostream>
#include <regex>
int main()
{
std::regex base64_regex(
"(?(DEFINE)"
"(?<B64>[A-Za-z0-9+/])"
"(?<B16>[AEIMQUYcgkosw048])"
"(?<B04>[AQgw])"
")"
"^("
"((?&B64){4})*"
"("
"(?&B64){4}|"
"(?&B64){2}(?&B16)=|"
"(?&B64)(?&B04)={2}"
")"
")?$");
// "Hello World!" base64 encoded
std::string base64 = "SGVsbG8gV29ybGQh";
if (std::regex_match(base64, base64_regex))
{
std::cout << "Match!" << std::endl;
}
else
{
std::cout << "No Match!" << std::endl;
}
}
but when I run the code I get an exception telling me it is not a valid regular expression.
Catching the exception and printing the "what" string doesn't help much either. All it gives me is the following:
regex_error(error_syntax)
Obviously I could get rid of the "DEFINE" block with my pre-defined subpatterns, but that would make the whole expression very difficult to read... and, well... I like to be able to maintain my own code when I come back to it a few years later lol so that isn't really a good option.
How can I get a similar regular expression to work in C++?
Note: This must all be done within a single "std::regex" object because I am writing a library where users will be able to pass a string to be able to define their own regular expressions and I want these users to be able to "DEFINE" similar subexpressions within their regex if they need to.
How about string concatenation?
#define B64 "[A-Za-z0-9+/]"
#define B16 "[AEIMQUYcgkosw048]"
#define B04 "[AQgw]"
std::regex base64_regex(
"^("
"(" B64 "{4})*"
"("
B64 "{4}|"
B64 "{2}" B16 "=|"
B64 B04 "={2}"
")"
")?$");
I took a suggestion from the comments and checked out "boost" regex since it supports "Perl" regular expressions. I gave it a try and it worked great!
#include <boost/regex.hpp>
boost::regex base64_regex(
"(?(DEFINE)"
"(?<B64>[A-Za-z0-9+/])"
"(?<B16>[AEIMQUYcgkosw048])"
"(?<B04>[AQgw])"
")"
"("
"((?&B64){4})*"
"("
"(?&B64){4}|"
"(?&B64){2}(?&B16)=|"
"(?&B64)(?&B04)={2}"
")"
")?", boost::regex::perl);
I want to implement following perl evaluation in boost regex or any other alternative in cpp.
#!/usr/bin/perl
use strict;
use warnings;
my $regex_pattern = "/^rst/i";
my $name = "rst";
my $match;
my $tmpRegExp = "\$match = (\$name =~ $regex_pattern);";
eval ($tmpRegExp);
if(!$match) {
print "not matched\n";
} else {
print "matched\n";
}
Perl coutput
% perl perl_regex.pl
matched
I tried by below sample code
#include <boost/regex.hpp>
#include <string>
#include <iostream>
int main()
{
std::string regex_pattern("/^rst/i");
std::string name("rst");
boost::regex regex_expr(regex_pattern, boost::regex::perl);
bool match = boost::regex_search(name, regex_expr);
if(match)
std::cout << "matched" << std::endl;
else
std::cout << "not matched" << std::endl;
return 0;
}
C++ Output
% g++ boost_regex.cpp -l boost_regex
% ./a.out
not matched
But this is not working as expected. I expected "matched" shall be the result for boost version also. this regex_pattern is a perl regex user variable.
Can someone help, where is the mistake?
According to this example in the documentation of the Boost regex feature, the pattern should not have slashes around it, and you cannot pass flags to the pattern within the pattern string like you would with the pattern creation operator m// in Perl.
regex expression("^([0-9]+)(\\-| |$)(.*)$");
Boost's documentation about PCRE says that by default, the pattern is case-sensitive. This supports my assumption that you cannot pass a flag like /i within the pattern itself. Instead, you need to pass it as a flag as the second argument to the pattern constructor as shown in the SYNOPSIS.
// e2 a case insensitive Perl regular expression:
boost::regex e2(my_expression, boost::regex::perl|boost::regex::icase);
A full list of those flags for PCRE within Boost is available here. Note that not all of these map to actual modifier flags that can be on m// or s/// in current Perls as described in perlre. That's because PCRE is not Perl, but rather the Perl Compatible Regex Engine.
There is a Standard Regex mechanism since C++11.
I personally would prefer this over boost or any other third party library. Of course that's only my own opinion.
If you want to use the utilities provided with C++11 you could do the following
#include <iostream>
#include <string>
#include <regex>
int main(int argc, char** argv)
{
std::string input = "rst";
std::regex regex_pattern("^rst", std::regex_constants::icase); // use ::icase to make the matching case insensitive like /i in perl
if ( std::regex_match(input, regex_pattern) )
{
std::cout << "matched!\n";
}
else
{
std::cout << "not matched!\n";
}
return 0;
}
I would like to use a regex both as a pattern to search and a template to construct a string. (I'm using boost::regex because I'm on gcc 4.8.4 where apparently regex is not fully supported (until 4.9)):
That is, I want to construct a regex, pass it to a function, use the regex to match some files, then construct an output file name following the same pattern. For example:
Regex: "file_.*\.txt"
to match things like "file_1.txt", "file_2.txt", etc.
and then would like to construct from it
Output: "file_all.txt"
That is, I want to match files starting with "file_" and ending with ".txt", then I want to fill in "all" between the "file_" and the ".txt", all from a single regex object.
We'll skip the matching to the regex as that is straightforward, but rather focus on the replacement:
#include <iostream>
#include <iterator>
#include <string>
#include <boost/regex.hpp>
std::string constructOutput(const boost::regex& myRegex)
{
// How to replace the match to the center of the filenames here?
// return boost::regex_replace(?, myRegex, "all");
}
int main()
{
// We can do something like this, but it requires us to manually separate the "center" of the regex from the string, as well as keep around a string object and a regex object:
// std::string myText = "File_.*.txt";
// boost::regex myRegex("_.*\\.");
// std::cout << '\n' << boost::regex_replace(myText, myRegex, "_all.") << '\n';
// Want to do this:
boost::regex myRegex("File_.*\\.txt");
std::string outputString = constructOutput(myRegex);
std::cout << outputString << std::endl;
}
Is something like this possible?
I'm failing to create a pattern for the stl regex_match function and need some help understanding why the pattern I created doesn't work and what would fix it.
I think the regex would have a hit for dl.boxcloud.com but it does not.
****still looking for input. I updated the program reflect suggestions. There are two matches when I think should be one.
#include <string>
#include <regex>
using namespace std;
wstring GetBody();
int _tmain(int argc, _TCHAR* argv[])
{
wsmatch m;
wstring regex(L"(dl\\.boxcloud\\.com|api-content\\.dropbox\\.com)");
regex_search(GetBody(), m, wregex(regex));
printf("%d matches.\n", m.size());
return 0;
}
wstring GetBody() {
wstring body(L"ABOUTLinkedIn\r\n\r\nwall of textdl.boxcloud.com/this/file/bitbyte.zip sent you a message.\r\n\r\nDate: 12/04/2012\r\n\r\nSubject: RE: Reference Ask\r\n\r\nOn 12/03/12 2:02 PM, wall of text wrote:\r\n--------------------\r\nRuba,\r\n\r\nI am looking for a n.");
return body;
}
There is no problem with the code itself. You mistake m.size() for the number of matches, when in fact, it is a number of groups your regex returns.
The std::match_results::size reference is not helpful with understanding that:
Returns the number of matches and sub-matches in the match_results object.
There are 2 groups (since you defined a capturing group around the 2 alternatives) and 1 match all in all.
See this IDEONE demo
#include <regex>
#include <string>
#include <iostream>
#include <time.h>
using namespace std;
int main()
{
string data("ABOUTLinkedIn\r\n\r\nwall of textdl.boxcloud.com/this/file/bitbyte.zip sent you a message.\r\n\r\nDate: 12/04/2012\r\n\r\nSubject: RE: Reference Ask\r\n\r\nOn 12/03/12 2:02 PM, wall of text wrote:\r\n--------------------\r\nRuba,\r\n\r\nI am looking for a n.");
std::regex pattern("(dl\\.boxcloud\\.com|api-content\\.dropbox\\.com)");
std::smatch result;
while (regex_search(data, result, pattern)) {
std::cout << "Match: " << result[0] << std::endl;
std::cout << "Captured text 1: " << result[1] << std::endl;
std::cout << "Size: " << result.size() << std::endl;
data = result.suffix().str();
}
}
It outputs:
Match: dl.boxcloud.com
Captured text 1: dl.boxcloud.com
Size: 2
See, the captured text equals the whole match.
To "fix" that, you may use non-capturing group, or remove grouping at all:
std::regex pattern("(?:dl\\.boxcloud\\.com|api-content\\.dropbox\\.com)");
// or
std::regex pattern("dl\\.boxcloud\\.com|api-content\\.dropbox\\.com");
Also, consider using raw string literal when declaring a regex (to avoid backslash hell):
std::regex pattern(R"(dl\.boxcloud\.com|api-content\.dropbox\.com)");
You need to add another "\" before each ".". I think that should fix it. You need to use escape character to represent "\" so your regex looks like this
wstring regex(L"(dl\\.boxcloud\\.com|api-content\\.dropbox\\.com)");
Update:
As #user3494744 also said you have to use
std::regex_search
instead of
std::regex_match.
I tested and it works now.
The problem is that you use regex_match instead of regex_search. To quote from the manual:
Note that regex_match will only successfully match a regular expression to an entire character sequence, whereas std::regex_search will successfully match subsequences
This fix will give a match, but too many since you also have to replace \. by \\. as shown before my answer. Otherwise the string "dlXboxcloud.com" will also match.