Regex in C++ how to search for valid Linux Device Node? - c++

Question

Given a device node in Linux such as "/dev/sda1" or "/dev/sdb", I'd like to match all valid choices to know if I have a valid device node.
Here's what I have so far:
static bool isUSBNameValid(const std::string &node) {
std::regex device("/dev/sd[a-z]*");
if (std::regex_match(node, device)) {
return true;
}
return false;
}
This does not work. Why is this?
How to make this work with any valid Linux device node?

Answer 1

Your /dev/sd[a-z]* pattern matches /dev/sd literal substring followed with any 0+ lowercase ASCII letters. Used within regex_match, the pattern must match the whole string. Since the /dev/sda1 ends with a digit, the regex_match fails, but it succeeds with /dev/sdb.
So, if you plan to only match SATA devices, you will need to use /dev/sd[a-z][0-9]* pattern, else, to match arbitrary number of alphanumeric chars after /dev/, you may use /dev/[[:alnum:]]+.
std::regex device_sata("/dev/sd[a-z][0-9]*");
std::regex device_any("/dev/[[:alnum:]]+");
See the C++ demo:
#include<regex>
#include <iostream>
using namespace std;
bool isUSBNameValid(const std::string &node, std::regex device) {
if (std::regex_match(node, device)) {
return true;
}
return false;
}
int main() {
std::regex device_sata("/dev/sd[a-z][0-9]*");
std::regex device_any("/dev/[[:alnum:]]+");
cout<< ( isUSBNameValid("/dev/sda1", device_sata) ? "Found" : "Not found")<<endl;
cout<< ( isUSBNameValid("/dev/sdb", device_sata) ? "Found" : "Not found")<<endl;
cout<< ( isUSBNameValid("/dev/ttyS0", device_any) ? "Found" : "Not found")<<endl;
return 0;
}

Answer 2

I would suggest the following pattern instead:
std::regex device("/dev/sd[a-z][0-9]*");
Add capturing groups around the [a-z] and [0-9]* if that becomes important.
If you truly want to match any device it would be:
std::regex device("/dev/[[::anum]]+");
with an additional check that what you have matched is not a directory. It would probably be good to add such a check (using stat) anyway.