The whole pattern therefore means one digit 0-9 followed by zero or many digits in the range 0-9.
so "3" would match "21" would match "123456" would match "" would not match
The obviously "correct" pattern for this behavior would be [0-9]+ The + means 1 or more and thus makes repeating the set obsolete.
Thanks!
You may wanna have a look at the PCRE flavor if you understand this you can work with all others (you'll only gonna miss some features)
The + is really just a shortcut for {1,} means 1 or more greedy the * is a shortcut for {0,} means 0 or more greedy Also while I'm at it the "even more correct" pattern ofc would be \d+ (at least in PCRE) \d stand for digit it shortcut for [0-9] Personally I would never write [0-9] I only ever use sets for partial ranges i.e. [5-9] or [a-f] Whenever you need the "full" set there is usually a short way to write it. This makes pattern shorter and easier to read. Another nice trick is to uppercase the shortcuts to invert it's meaning so \D would match any non-digit.
https://www.gnu.org/software/sed/manual/html_node/BRE-syntax...
[0|1|2|3|4|5|6|7|8|9][0|1|2|3|4|5|6|7|8|9]{0,} and [0-9][0-9]* and [0-9]+ and \d+ all do the same so they are not wrong as in the result will be correct.
>Regex For Noobs (like me!) - an illustrated guide
So I am painfully aware that I'm a noob too, I even call myself one! I wrote this little piece because I felt that regex can be kind of intimidating for a lot of people but that it's actually pretty OK and fun once you get the hang of it. To get people over that initial barrier is what I aim to do with the "guide".
I can recommend the articles by Julia Evans[1], which are pretty much like this. She works on a problem that is new to her and describes how she solved it or how she learned something new.
[1]: https://jvns.ca/