Check if variable matches pattern, LUA - lua

Question

So if I have the variable name. How can I check if it matches a pattern?
For instance, I would like to check if the variable name equals a pattern like text_text. So words at the beginning then underscore then words. With no numbers.
I really have no idea where to even start with this.
local pattern = something
if name == pattern then
UPDATE** I have tried the following, still nothing is working.
local pattern = "a%%sa%"
if string.match (name, pattern) then
return 1
else
return 0
end
Also tried this way
local pattern = "a%_a%"
if string.match (name, pattern) then
return 1
else
return 0
end
Can I please get some help

Answer 1

A pattern that matches any combination of small letters linked with an underscore would be:
"%l+_%l+"
%l specifies any lower case letter,
followed by a + which specifies the number of the symbol it follows.
So %l+ means "at least one lower case letter"
_ is simply an underscore.
So the pattern "%l+_%l+" means "at least one lower case letter followed by one underscore followed by at least one lower case letter
Please refer to https://www.lua.org/pil/20.2.html and/or https://www.lua.org/manual/5.3/manual.html#6.4.1 for all the possible bricks you can construct patterns of.
You can use those patterns in the functions provided by the string standard library. string.find, string.gsub and so on.
If you want to use that stuff more excessively checkout LPeg for example.

Answer 2

Try this:
function match(string)
local string = string:match('^(%a+_%a+)$')
if string then
return true
else
return false
end
end
local string = match('hi I'm webrom')
print(string)
output = false
local string = match('14545_15456')
print(string)
output = false
local string = match('hello_world')
print(string)
output = true
local string = match('HELLO_WORLD')
print(string)
output = true
The pattern %a match any letter.

Answer 3

in string patterns in lua,
anything between parantheses will be returned
also you do % with a special caracter afterwards like a for letters, to match ONE letter
adding + after %a would make you detect THE MOST possible letters , in the pattern before you get to the next character / set of characters
for example :
s = "Hello Julia my love ! Here's a hug!"
lovername,gift = string.match(s,"(%a+) my love ! Here's a (%a+)")
print(lovername.." was given a "..gift)
In your example, you can do this :
var = "hello_world"
if (string.match(var, "%a+_%a+")) then -- In this example, _ will be normal
print("Valid variable name !")
else
print("Invalid variable name")
end