I have two strings - each string has many lines like the following:
string1 = " DEFAULT-VLAN | Manual 10.1.1.3 255.255.255.0 "
string2 = " 1 DEFAULT-VLAN | Port-based No No"
The first string I split into the following strings: "DEFAULT-VLAN", "|", "Manual"...
Then I want to look up the ID ("1") in string2 for the vlanName ("DEFAULT-VLAN") from string1.
I use this code to find the correct substring:
vpos1, vpos2 = vlan:find("%d-%s-" .. vlanName .. "%s-|")
But vpos1 and vpos2 are nil; When the hyphen ("-") is deleted from the vlanName it is working.
Shouldn't Lua take care to escape the special characters in such strings? The string is handed over from my C++ application to Lua and there may be lots of special characters.
Is there an easy way to solve this?
Thanks!
Lua is not magic. All the expression "%d-%s-" .. vlanName .. "%s-|" does is concatenate some strings, producing a final string. It has no idea what that string is intended to be used for. Only string.find knows that, and it can't have any affect on how the parameter it is given will be used.
So yes, vlanName will be interpreted as a Lua pattern. And if you want to use special characters, you will need to escape them. I would suggest using string.gsub for that. It'd be something like this:
vlanName:gsub("[%-...]", "%%%0")
Where ... are any other characters you want to escape.
Related
I'm trying to use the regex /^[a-zA-Z0-9_$&+:;=?##|'<>.^*()%!-]+$/ with dart regex. I've seen you can use raw strings. So Ive put the above in between r'' like this:
r'^[a-zA-Z0-9_$&+:;=?##|'<>.^*()%!-]+$' but the ' is messing it up. How do I tell dart this is a special character..
EDIT
I tried this but it doesn't seem to work
static final RegExp _usernameRegExp = RegExp(
r"^[a-zA-Z0-9_$&+:;=?##|'<>.^*()%!-]+$",
);
So I have a TextField with a text controller for a username. A method like this
static bool isValidUsername(String username) {
return (_usernameRegExp.hasMatch(username));
}
I pass the controller.text as the username.
I've a function:
bool get isUserNameValid => (Validators.isValidUsername(userNameTextController.text.trim()));
I can type all the given characters in to the textbook but not '
Your RegExp source contains ', so you can't use that as string delimiter without allowing escapes. It also contains $ so you want to avoid allowing escapes.
You can use " as delimiter instead, so a raw string like r"...".
However, Dart also has "multi-line strings" which are delimited by """ or '''. They can, but do not have to, contain newlines. You can use those for strings containing both ' and ". That allows r'''...'''.
And you can obviously also use escapes for all characters that mean something in a string literal.
So, for your code, that would be one of:
r'''^[\w&+:;=?##|'<>.^*()%!-]+$'''
r"^[\w&+:;=?##|'<>.^*()%!-]+$"
'^[\\w&+:;=?##|\'<>.^*()%!-]+\$'
(I changed A-Za-z0-9$_ to \w, because that's precisely what \w means).
In practice, I'll always use a raw string for regexps. It's far too easy, and far too dangerous, to forget to escape a backslash, so use one of the first two options.
I'd probably escape the - too, making it [....\-] instead of relying on the position to make it non-significant in the character class. It's a fragile design that breaks if yo add one more character at the end of the character class, instead of adding it before the -. It's less fragile if you escape the -.
How to print all special characters without inserting escape sign before every of them? I have very large textiles with many special characters and I'm looking for something like # in c# which prints string literally as it is
What you're referring to, is called a verbatim string literal in C# and that concept does not translate exactly to Swift.
However, with the introduction of multiline string Literals in Swift 4, you can get close.
let multilineString = """
Here you can use \ and newline characters.
Also single " or double "" are allowed.
"""
For reference, find the grammar of a Swift String literal here.
I want to define an array in ruby in following manner
A = ["\"]
I am stuck here for hours now. Tried several possible combinations of single and double quotes, forward and backward slashes. Alas !!
I have seen this link as well : here
But couldn't understand how to resolve my problem.
Apart from this what I need to do is -
1. Read a file character by character (which I managed to do !)
2. This file contains a "\" character
3. I want to do something if my array A includes this backslash
A.includes?("\")
Any help appreciated !
There are some characters which are special and need to be escaped.
Like when you define a string
str = " this is test string \
and this contains multiline data \
do you understand the backslash meaning here \
it is being used to denote the continuation of line"
In a string defined in a double quotes "", if you need to have a double quote how would you doo that? "\"", this is why when you put a backslash in a string you are telling interpretor you are going to use some special characters and which are escaped by backslash. So when you read a "\" from a file it will be read as "\" this into a ruby string.
char = "\\"
char.length # => 1
I hope this helps ;)
Your issue is not with Array, your question really involves escape sequences for special characters in strings. As the \ character is special, you need to first prepend it (escape it) with a leading backslash, like so.
"\\"
You should also re-read your link and the section on escape sequences.
You can escape backslash with a backslash in double quotes like:
["\\"].include?("\\")
I have a String like
file:c:\test\xyz.exe
how can I separate the above string in 3 parts through Regex in Lua?
For the example, the first part would be file:,
the second part of string should be c:\test
and the third part of string should be yz.exe.
have a look at the String manipulation part of the Lua manual : http://www.lua.org/manual/5.1/manual.html#5.4
In particular match() and gmatch(). For example :
s = "file:c:\\test\\xyz.exe"
for first, second, third in string.gmatch(s, "(%a+):(.+)\\([%a%p]+)") do
print(first)
print(second)
print(third)
end
To allow alphanumerical character in the first and third place, replace %a with %w. All others possible pattern are referenced at the end of the linked manual chapter.
You must double each '\' in your input string, otherwise pattern matching won't work. Backslash is an escaping character in Lua, so if you want to have one in your string, you must escape it : "\\"
The given code will work for "file:c:\test\xyz.exe" and "file:C:\test\test3\a\abc.exe"
Could anybody help me make a proper regular expression from a bunch of text in Ruby. I tried a lot but I don't know how to handle variable length titles.
The string will be of format <sometext>title:"<actual_title>"<sometext>. I want to extract actual_title from this string.
I tried /title:"."/ but it doesnt find any matches as it expects a closing quotation after one variable from opening quotation. I couldn't figure how to make it check for variable length of string. Any help is appreciated. Thanks.
. matches any single character. Putting + after a character will match one or more of those characters. So .+ will match one or more characters of any sort. Also, you should put a question mark after it so that it matches the first closing-quotation mark it comes across. So:
/title:"(.+?)"/
The parentheses are necessary if you want to extract the title text that it matched out of there.
/title:"([^"]*)"/
The parentheses create a capturing group. Inside is first a character class. The ^ means it's negated, so it matches any character that's not a ". The * means 0 or more. You can change it to one or more by using + instead of *.
I like /title:"(.+?)"/ because of it's use of lazy matching to stop the .+ consuming all text until the last " on the line is found.
It won't work if the string wraps lines or includes escaped quotes.
In programming languages where you want to be able to include the string deliminator inside a string you usually provide an 'escape' character or sequence.
If your escape character was \ then you could write something like this...
/title:"((?:\\"|[^"])+)"/
This is a railroad diagram. Railroad diagrams show you what order things are parsed... imagine you are a train starting at the left. You consume title:" then \" if you can.. if you can't then you consume not a ". The > means this path is preferred... so you try to loop... if you can't you have to consume a '"' to finish.
I made this with https://regexper.com/#%2Ftitle%3A%22((%3F%3A%5C%5C%22%7C%5B%5E%22%5D)%2B)%22%2F
but there is now a plugin for Atom text editor too that does this.