What is [50-99] in regular expression?

[shivajikobardan]

TL;DR Summary

regular expression character set meaning for [50-99]?

As the slide says, it's not 50-99 characters so what it is?

Source: https://www3.cs.stonybrook.edu/~pfodor/courses/CSE307/L02_Programming_RE.pdf

Also, please tell me how to learn regular expressions? Recommend some university/any courses to take for learning regular expression for backend development. (Not the one we learnt in theory of automata and computation).

There are lots of resources to learn it like regexpal for testing regular expressions, regexone.com for learning it. But how'd you learn it? Like what process do you follow to learn it?

 

[pbuk]

TL;DR Summary: regular expression character set meaning for [50-99]?

As the slide says, it's not 50-99 characters so what it is?

The answer is in the slide: [50-99] is the same as [0-9]. Why do you think this is?

Spoiler

[5] matches a 5, [9] matches a 9, [59] matches a 5 or a 9, [0-9] matches any character 0-9

regexone.com for learning it. But how'd you learn it? Like what process do you follow to learn it?

I had not seen https://regexone.com/ before: it looks really good so learn from that.

 

[Mark44]

A key idea on the page about character ranges is this:

represent all characters between two characters

So 50 and 99 are not treated as numbers, but rather as a pair of characters each,

 

[shivajikobardan]

but I tried in regexpal, [50-99] matches number between 50-99 as well? @pbuk

edit: I'm wrong it also matches 98888

 

[shivajikobardan]

I got it. it's [5,0-9,9] that's why.