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?("\\")
Related
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.
Does anyone understand what this (([A-Za-z\\s])+)\\? means?
I wonder why it should be "\\s" and "\\" ?
If I entered "\s", Xcode just doesn't understand and if I entered "\?", it just doesn't match the "?".
I have googled a lot, but I did not find a solution. Anyone knows?
The actual regex is (([A-Za-z\s])+)\?. This matches one or more letters and whitespace characters followed by an question mark. The \ has two different meanings here. In the first instance \s has a fixed meaning and stands for any white space characters. In the second instance the \? means the literal question mark character. The escaping is necessary as the question mark means one or none of the previous otherwise.
You can't type your regex like this in a string literal in C code though. C also does some escaping using the backslash character. For example "\n" is translated to a string containing only a newline character. There are some other escape sequences with special meanings. If the character after the backslash doesn't have a special meaning the backslash is just removed. That means if you want to have a single backspace in your string you have to write two.
So if you wrote your regex string as you wanted you'd get different results as it would be interpreted as (([A-Za-zs])+)? which has a completely different meaning. So when you write a regex in an ObjC (or any other C-based language) string literal you must double all backslash characters.
not sure about ios but same thing happens in java. \ is escape character for java,and c also so when you type \s java reads \ as an escape character.
think of it as if you want to print a \ what will you have to do.
you will have to type \\. now first \ will work as escape character for java and second one will be printed.
I think it should be the same concept for ios too.
so if you want \s you type \s, if you want \ you type \\.
The \s metacharacter is used to find a whitespace character.
Refer this!
I have tried to print it but it just by passes because it's an escaped character.
e.g output should be as follows.
\correct
For that and also future reference:
\0 – Null character (that is a zero after the slash)
\\ – Backslash itself. Since the backslash is used to escape other characters, it needs a special escape to actually print itself.
\t – Horizontal tab
\n – Line Feed
\r – Carriage Return
\” – Double quote. Since the quotes denote a String literal, this is necessary if you actually want to print one.
\’ – Single Quote. Similar reason to above.
Use the following code for Swift 5, Xcode 10.2
let myText = #"This is a Backslash: \"#
print(myText)
Output:
This is a Backslash: \
Now not required to add a double slash to use a single slash in swift 5, even now required slash before some character, for example, single quote, double quote etc.
See this post for latest update about swift 5
https://www.hackingwithswift.com/articles/126/whats-new-in-swift-5-0
var s1: String = "I love my "
let s2: String = "country"
s1 += "\"\(s2)\""
print(s1)
It will print I love my "country"
The backslash character \ acts as an escape character when used in a string. This means you can use, for example, double quotes, in a string by pre-pending them with \. The same also applies for the backslash character itself, which is to say that println("\\") will result in just \ being printed.
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.
How do I remove this backslash?
s = "\""
I have tried s.gsub("\\", "") and that doesn't remove it, it returns the same string.
there's actually no backslash character in your String. The Backslash in your example simply escapes the following double quote and prevent's that it would terminate the string and thereby resulting in a syntax error (unterminated double quote ).
So what you see when you print that string in IRB is actually not the backslash as is, but the backslash in combination with the following dobule quote as an indication that the double quote is escaped. Kind of hard to grasp when you encounter it the first time. Have a look at http://en.wikibooks.org/wiki/Ruby_Programming/Strings#Escape_sequences
long story short: there is no backslash in your string so you can't remove it :)
gsub takes a regular expression as the first parameter. I believe that if you pass it a string, it will first convert it into a regex. This means you need extra escaping:
s.gsub("\\\\", "")
If you use regex notation, you can stop it from doubling up:
s.gsub(/\\/, "")
This is because you don't have to escape twice: once because double-quoted strings need you to escape the \ character, and once because the regular expression requires you to as well.
that's actually an escape quote sign (do a print s to see it)
I'm not sure if this is a solution to YOUR problem, but seeing that this is one of the first SO questions I looked at when trying to solve my problem and have in fact, solved it, here is what I did to fix my problem.
So I had some CSV.read output with a load of \ (backslashes) and unwanted quotation marks.
arr_of_arrays = CSV.read("path/to/file.csv")
processed_csv = arr_of_arrs.map {|t| eval(t)}
the key here is the eval() method.