This is probably a rather trivial question for the Erlang experts - I'm trying to have my ejabberd server store offline messages (in a Riak db) which inherently do contain double quotes (") around various values, etc. I get a format error when I try to create a Riak database object from them, and testing of replacing the double quotes with an escape character (\") corrects the issue. The question is how can I do this replacement manually?
I tried the following code but somehow doesn't work.
(ejabberd#xxx-xx-xx-xxx)4> re:replace(""hello"", """, "\"", [{return, list}, global]).
* 1: syntax error before: hello
So essentially I'm trying to replace the embedded " around the hello word with \".
I don't know Erlang, but you probably need something like this:
"\"hello\"", "\"", "\\\""
You must escape both " and \ in replacement string.
The Erlang literal syntax for strings uses the "\" (backslash)
character as an escape code. You need to escape backslashes in literal
strings, both in your code and in the shell, with an additional
backslash, i.e.: "\".
Example:
Let's make an example. I use $ Erlang symbol which will be substituted with ascii integer of a character to show what is happening behind each string which basically is a list of integer.
Subject = [$"] ++ "hello" ++ [$"] = "\"hello\"".
Target = [$"] = "\"".
Replacement = [$\\, $\\, $"] = "\\\\\"".
Result = re:replace(Subject, Target, Replacement, [{return, list}, global]).
Now with getting the length of Subject and Result we can find the difference:
7 = length(Subject). %% => 7 characters: " h e l l o "
9 = length(Result). %% => 9 characters: \ " h e l l o \ "
Related
I am working on a project, in which you type your input sentence, and I need to be able to use " and ' in the sentence, such as Input = "I said, "Hi what's up?" print(Input) in which I get an error. If anyone knows how to fix this that would be great.
See https://www.lua.org/pil/2.4.html. Lua has very interesting feature to declare string with square brackets:
input = [[I said, "Hi what's up?"]]
input = "I said, \"Hi what's up?\""
input = 'I said, "Hi what\'s up?"'
I will tell some things in addition to what #Darius told above
When you tried to add a quatation mark inside a string, the lua interpreter get confused and break your string after the next quation mark without reaching the end of the line. That's the reason for the error.
Try to understand it by the following code
str = "Hello I"m somebody" -- here the interpreter will think str equals to "Hello I" at first, and then it will find some random characters after which may make it confused (as m somebody is neither a variable nor a keyword)"
-- you can also see the way it got confused by looking at the highlighted code
--What you can do to avoid this is escaping the quotes
str = "Hello I\"m somebody" -- here the interpreter will treat \" as a raw character (") and parse the rest.
You can also use the escape character () with others such as \', \", \[, \n (newline character), \t (tab) and so on.
How do we ignore backslashes in a string?
I tried this but it dosen't work:
let str2 = #"I igonore \ \ \ / / / / backsalshes"
printfn "%s" str2
Also, I thought ignoring double quotes in a string is as follow:
let str3 = """ "I ig""onore double quotes and backslasehes " """
printfn "%s" str3
Again, It printed a string with the double quote 'ig""onore'.
What is wrong?
The # sign doesn't "ignore" backslashes in the sense that they don't appear in the string, it simply treats them as normal characters, instead of as characters with a special meaning. E.g.,
let s1 = "\n" # A single newline character
let s2 = #"\n" # Two characters, a backslash and then a lowercase n
Likewise, the triple-quote syntax doesn't make " characters disappear, it simply lets you embed single " characters, or pairs of them, in the string without having to jump through syntax hoops to do so. If it make " characters disappear in a string, it wouldn't be very useful.
I have this lines of code in ejabberd module, it works fine:
case catch ejabberd_odbc:sql_query(Server,["select COUNT(*) as total from spool where username='",IdUsername,"' AND xml LIKE '%message from%' AND xml LIKE '%chat%';"]) of
{selected, [<<"total">>], [[Totale]]} ->
Count = binary_to_list(Totale);
_ -> Count = "0"
end,
If I convert this:
LIKE '%chat%';
with this:
LIKE '%type=\'chat\'%';
I obtain an error, any ideas? or there's another way to get only the chat message?
Since you're typing this in an Erlang string, the Erlang escape sequences apply. In particular, \' is an escape sequence for just a single quote, '. (That's more useful inside atoms, which are delimited by single quotes.)
You can try it in an Erlang shell, and see that "\'" and "'" are equivalent:
1> "\'".
"'"
2> "\'" =:= "'".
true
To include an actual backslash in the string, escape it with another backslash:
"\\'"
In your case, that would be:
LIKE '%type=\\'chat\\'%';
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?("\\")
English isn't my mother tongue,so it's a little hard to describe the question.
I wanna to get 'd=40' in str by lua string.gsub(),but there's some problem.
------code below---
local str =
[==[
-- a=10
- -b=20
--c=30
d=40
]==]
local pat1 = [=[%s[%s]]=]
local pat2 = [=[\n[%s]]=]
str:gsub(pat1, function(s) print("pat1>>" .. s) end) --pat1>>d=40
str:gsub(pat2, function(s) print("pat2<<" .. s) end) --not match
local re1,_ = str:gsub("\n","$")
local re2,_ = str:gsub("%s","$")
print(re1) --a=10$- -b=20$ --c=30$d=40$
print(re2) --$a=10$-$-b=20$$ --c=30$d=40$
As Lua 5.1 Reference Manual Say
%s: represents all space characters.
I Think it equal to '\n',' 'and'\t'.
Question : Why pat2 can't match?
But I think pat2 is right,there's a '\n'befor'd=40' ,
so I think It can match ,but it can't work,why?
When you use [[]] notation for strings, that's a special string literal that takes the string exactly as you provide it. No character escaping is done. You can put some number of = characters in the brackets, to make it a bit easier to let you use [ characters in the string.
The string literal "\n" is one character, representing the newline. That's because of the use of the escape character \. The escape character applied to the 'n' character means "the newline character."
The string literal [[\n]] is exactly what it says: the character '\' followed by the character 'n'. Because no escaping is done, \n is not treated specially. It's exactly what it looks like.
Therefore, when you say local pat2 = [=[\n[%s]]=] You're saying "the first character should be '\' followed by 'n' followed by a space. That's not what you want; you want the escaping to work. So you should use a regular string literal: local pat2 = "\n[%s]".