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!
Related
Which Ansi escape sequence is the most portable and/or simply best and why?
1. "\u001B[32;1mThis is bright green\u001B[0m"
2. "\x1B[33;1mThis is bright yellow\x1B[0m"
3. "\e[35;4;1mThis is bright purple underlined\e[0m"
I have been using printf "\x1B[32;1mgreen\x1B[0m" (that's an example in unix bash script for example) out of habit, but I was wondering if there were any reasons to use one over the other. Is one more portable than the others? That would be my assumption.
Also, if you know of any other Ansi Escape sequence feel free to share it in the comments or at the end of your answer.
If you don't know what an Ansi Escape sequence is or want to become more familiar with it, then here you go: http://en.wikipedia.org/wiki/ANSI_escape_code
NOTE:
All of the escape sequences above have worked on all of the Unix systems I have been on, however one must still rely on the system itself to interpret the escape codes. Windows, for example, does not permit any sort of escape codes except four (BEL, L-F or linefeed, C-R or carriage return and, of course, BS or backspace), so Ansi escape sequences will not work.
Short answer: It depends on the host string parser.
Long answer:
It depends on the string parser; that is, the piece of code that actually takes in your string ("\x1b[1mSome string\x1b[0m") as a literal and parses the escape characters using the backslash ANSI escape sequence.
For parsers that support hexadecimal escapes (\x), then \x1b (character 0x1B) should work.
For parsers that support octal escapes (\ddd), then \033 (octal 33) should work.
For parsers that support unicode escapes (\u), then \u001B should work.
Quick elaboration: \x and \u are similar; \x usually refers to a single character, 0-255, in hexadecimal radix. \u means the same (as it is represented in hexadecimal), but supports two bytes (in most parsers) and generally refers to 16-bit unicode characters.
A lesser used/supported escape character, as you mentioned, is \e. This escape is most commonly used with parsers/languages that expect a lot of ANSI escaping to happen, such as bash (and most other shells).
For instance, Node.js does not support \e:
> console.log("\x1b[31mhello\x1b[0m")
hello
undefined
> console.log("\e[31mhello\e[0m")
e[31mhelloe[0m
undefined
Neither does Lua:
> print('\x1b[31mhello\x1b[0m')
hello
> print('\e[31mhello\e[0m')
stdin:1: invalid escape sequence near '\e'
Or even Python:
>>> print("\x1b[31mhello\x1b[0m")
hello
>>> print("\e[31mhello\e[0m")
\e[31mhello\e[0m
>>>
Though PHP does:
<?php
echo "\x1b[31mhello\x1b[0m\n"; // hello
echo "\e[31mhello\e[0m\n"; // hello
Currently I am learning how to work with HL7 and how to parse it in python. Now I was wondering what happens if a value in a HL7 segment contains a pipe sign, e.g. '|'. How is this sign handled? If there is no masking, it would lead to a crash of the HL7 parser. Is there a masking possibility?
\F\
You should read the relevant sections of chapter 2 of the version 2 standard about how escaping works in version 2.
The HL7 structure has defined escape sequences for the separators like |.
When you look at a HL7 message, the used five delimiters are right after the MSH:
MSH|^~\&
| is the Field separator F
^ the component separator S
~ is the repetition separator (for the second level elements) R
\ is the escape character E
& is the sub-component separator T
So to escape one of the special characters like |, you have to take the escape character and then add the defined letter (F,S, etc.)
So in above case, to escape the | you would have to put \F\. Or escaping the escape character is \E\.
If you like you can also change the delimiters after the MSH completely, but I don't recommend that.
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 seen the following on StackOverflow about URL characters:
There are two sets of characters you need to watch out for - Reserved and Unsafe.
The reserved characters are:
ampersand ("&")
dollar ("$")
plus sign ("+")
comma (",")
forward slash ("/")
colon (":")
semi-colon (";")
equals ("=")
question mark ("?")
'At' symbol ("#").
The characters generally considered unsafe are:
space,
question mark ("?")
less than and greater than ("<>")
open and close brackets ("[]")
open and close braces ("{}")
pipe ("|")
backslash ("\")
caret ("^")
tilde ("~")
percent ("%")
pound ("#").
I'm trying to code a URL so I can parse it using delimiters. They can't be numbers or letters though. Does anyone have a list of characters that are NOT Reserved but ARE safe to use?
Thanks for any help you can provide.
Don't bother trying to use safe/unreserved characters. Just use whatever delimiters you want and URLencode the whole thing. Then URL decode it on the other end and parse normally.
Is there a reason you can't just use the standard delimiter for URL parameters (&)? That is the most straightforward way to do it instead of trying to roll your own.
For example the standard URL syntax already allows for multi-valued paramaters natively. This is perfectly legal and doesn't require any trickery.
Somepage.aspx?parameterName=A¶meterName=B
The result is that the page would be passed "A,B" in the parameterName attribute.
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.