I'm trying to find the hexadecimal non-printable character 00h within a string with Lua. I tried it with an escape character and as a result I get the same location I start in (that's a printable character). I fiddled around with the character classes, but that didn't amount to anything. My approach looks like this:
location = string.find(variable,"\00",startlocation)
I also tried it this way, but no luck:
location = string.find(variable, string.char(00),startlocation)
How can I find this non-printable pattern in Lua?
It works fine for me:
> return string.find("one\0two\0,three","\0,")
8 9
> return string.find("one\0two\0,three","\0")
4 4
> return string.find("one\0two\0,three","\00")
4 4
> return string.find("one\0two\0,three","\00",6)
8 8
Related
I'm trying to take decimal number as an input and I need output of all numbers but without the point symbol in it.
Example input: 123.4
Wanted output 1234
The problem I have that when converting decimal number into string and trying to remove "." using :gsub('%.', '') its removing the point symbol but outputs 1234 1 .
I have tried :gsub('.', '') as well but it outputs 5.
I'm clueless where those numbers come from, here is the screenshot:
Use this syntax to get what you want and discard/ignore what you dont need...
local y = 123.4
-- Remove decimal point or comma here
local str, matches = tostring(y):gsub('[.,]', '')
-- str holds the first return value
-- The second return value goes to: matches
-- So output only the string...
print(str) -- Output: 1234
-- Or/And return it...
return str
There are two issues at play here:
string.gsub returns two values, the resulting string and the number of substitutions. When you pass the results of gsub to print, both will be printed. Solve this by either assigning only the first return value to a variable (more explicit) or surrounding gsub with parenthesis.
. is a pattern item that matches any character. Removing all characters will leave you with the empty string; the number of substitutions - 5 in your example - will be the number of characters. To match the literal dot, either escape it using the percent sign (%.) or enclose it within a character set ([.]), possibly adding further decimal separators ([.,] as in koyaanisqatsi's answer).
Fixed code:
local y = 123.4
local str = tostring(y):gsub("%.", "") -- discards the number of substitutions
print(str)
this is unreliable however since tostring guarantees no particular output format; it might as well emit numbers in scientific notation (which it does for very large or very small numbers), causing your code to break. A more elegant solution to the problem of shifting the number such that it becomes an integer would be to multiply the number by 10 until the fractional part becomes zero:
local y = 123.4
while y % 1 ~= 0 do y = y * 10 end
print(y) -- note: y is the number 1234 rather than the string "1234" here
I was playing around with some patterns today to try to match some specific characters in a string, and ran into something unusual that I'm hoping someone can explain.
I had created a set looking for a list of characters within some strings, and noticed I was getting back some unexpected results. I eliminated the characters in the set until I got down to just three, and it seems to be these three that are responsible:
string = "alpha.5dc1704B40bc7f.beta.123456789.gamma.987654321.delta.abc123ABC321"
result = ""
for a in string.gmatch(string, '[+-_]') do
result = result .. a .. " "
end
> print(result)
. 5 1 7 0 4 B 4 0 7 . . 1 2 3 4 5 6 7 8 9 . . 9 8 7 6 5 4 3 2 1 . . 1 2 3 A B C 3 2 1
Why are these characters getting returned here (looks like any number or uppercase letter, plus dots)? I note that if I change up the order of the set, I don't get the same output - '[_+-]' or '[-_+]' or '[+_-]' or '[-+_]' all return nothing, as expected.
What is it about '[+-_]' that's causing a match here? I can't figure out what I'm telling lua that is being interpreted as instructions to match these characters.
When a - is between other characters inside square brackets, it means everything between those two. For example, [a-z] is all of the lowercase letters, and [A-F] is A, B, C, D, E, and F. [+-_] means every ASCII character between + and _, which includes all the numbers, all the uppercase letters, and a lot of punctuation.
Currently I have code that looks like this:
somestring = "param=valueZ&456"
local stringToPrint = (somestring):gsub("(param=)[^&]+", "%1hello", 1)
StringToPrint will look like this:
param=hello&456
I have replaced all of the characters before the & with the string "hello". This is where my question becomes a little strange and specific.
I want my string to appear as: param=helloZ&456. In other words, I want to preserve the character right before the & when replacing the string valueZ with hello to make it helloZ instead. How can this be done?
I suggest:
somestring:gsub("param=[^&]*([^&])", "param=hello%1", 1)
See the Lua demo
Here, the pattern matches:
param= - literal substring param=
[^&]* - 0 or more chars other than & as many as possible
([^&]) - Group 1 capturing a symbol other than & (here, backtracking will occur, as the previous pattern grabs all such chars other than & and then the engine will take a step back and place the last char from that chunk into Group 1).
There are probably other ways to do this, but here is one:
somestring = "param=valueZ&456"
local stringToPrint = (somestring):gsub("(param=).-([^&]&)", "%1hello%2", 1)
print(stringToPrint)
The thing here is that I match the shortest string that ends with a character that is not & and a character that is &. Then I add the two ending characters to the replaced part.
I'm trying to parse a text file using lua and store the results in two arrays. I thought my pattern would be correct, but this is the first time I've done anything of the sort.
fileio.lua:
questNames = {}
questLevels = {}
lineNumber = 1
file = io.open("results.txt", "w")
io.input(file)
for line in io.lines("questlist.txt") do
questNames[lineNumber], questLevels[lineNumber]= string.match(line, "(%a+)(%d+)")
lineNumber = lineNumber + 1
end
for i=1,lineNumber do
if (questNames[i] ~= nil and questLevels[i] ~= nil) then
file:write(questNames[i])
file:write(" ")
file:write(questLevels[i])
file:write("\n")
end
end
io.close(file)
Here's a small snippet of questlist.txt:
If the dead could talk16
Forgotten soul16
The Toothmaul Ploy9
Well-Armed Savages9
And here's a matching snippet of results.txt:
talk 16
soul 16
Ploy 9
Savages 9
What I'm after in results.txt is:
If the dead could talk 16
Forgotten soul 16
The Toothmaul Ploy 9
Well-Armed Savages 9
So my question is, which pattern do I use in order to select all text up to a number?
Thanks for your time.
%a matches letters. It does not match spaces.
If you want to match everything up to a sequence of digits you want (.-)(%d+).
If you want to match a leading sequence of non-digits then you want ([^%d]+)(%d+).
That being said if all you want to do is insert a space before a sequence of digits then you can just use line:gsub("%d+", " %0", 1) to do that (the one to only do it for the first match, leave that off to do it for every match on the line).
As an aside I don't think io.input(file) is doing anything useful for you (or what you might expect). It is replacing the default standard input file handle with the file handle file.
I'm new in Lua and looking for internet I don't find a solution to my problem, or an answer if I actually can do the next thing.
I have the next table. As you can see the key has a í:
DB = {
["Vigía"] = 112
}
If I try to retrieve that value from the table it returns nil.
I tried removing the í character and then I can get the value 112.
Can I use latin characters as a key in this scenario?,
Thanks!
You should be able to, but there are some caveats (lua-users.org)
I've run your code at ideone, and it works fine. Perhaps your editor is doing something weird? What version of Lua are you using?
DB = {
["Vigía"] = 112
}
print(DB["Vigía"])
print(_VERSION)
Result:
Success time: 0.02 memory: 2540 signal:0
112
Lua 5.1