I always thought that '' and "" were the same in pig, but today I got the
Unexpected character '"'
error on
register datafu-pig-1.2.1.jar
define Coalesce datafu.pig.util.Coalesce;
...
Coalesce(x,"a")
while
Coalesce(x,'a')
works just fine.
So, what is the difference between single and double quotes?
Pig doesn't support double quotes for string literals(ie chararray). All the chararray must be enclosed within single quotes.
A String or Chararrays are represented in interfaces by java.lang.String.
Constant chararrays are expressed as string literals with single quotes, for example, 'fred'
Reference:http://chimera.labs.oreilly.com/books/1234000001811/ch04.html#scalar_types
Related
The Redshift doc for the QUOTE_IDENT function says
The QUOTE_IDENT function returns the specified string as a string in double quotation marks so that it can be used as an identifier in a SQL statement. Appropriately doubles any embedded double quotation marks.
I understand the first part about surrounding a string with double quotation marks. But when is it appropriate to double embedded quotation marks? Why is that useful?
when is it appropriate to double embedded quotation marks? Why is that useful?
It's always appropriate. It's useful because the output of QUOTE_IDENT is often embedded into a larger string. As such, you then have a quoted string inside the larger string and you detect the end of such a string by finding a single double quote. I.e. assume we pass AB"CD to QUOTE_IDENT. We receive back "AB""CD". We then embed that into:
SELECT "AB""CD" FROM Foo
And when that's parsed later, we find a single identifier AB"CD in the SELECT list.
I tried many ways to get a single backslash from an executed (I don't mean an input from html).
I can get special characters as tab, new line and many others then escape them to \\t or \\n or \\(someother character) but I cannot get a single backslash when a non-special character is next to it.
I don't want something like:
str = "\apple"; // I want this, to return:
console.log(str); // \apple
and if I try to get character at 0 then I get a instead of \.
(See ES2015 update at the end of the answer.)
You've tagged your question both string and regex.
In JavaScript, the backslash has special meaning both in string literals and in regular expressions. If you want an actual backslash in the string or regex, you have to write two: \\.
The following string starts with one backslash, the first one you see in the literal is an escape character starting an escape sequence. The \\ escape sequence tells the parser to put a single backslash in the string:
var str = "\\I have one backslash";
The following regular expression will match a single backslash (not two); again, the first one you see in the literal is an escape character starting an escape sequence. The \\ escape sequence tells the parser to put a single backslash character in the regular expression pattern:
var rex = /\\/;
If you're using a string to create a regular expression (rather than using a regular expression literal as I did above), note that you're dealing with two levels: The string level, and the regular expression level. So to create a regular expression using a string that matches a single backslash, you end up using four:
// Matches *one* backslash
var rex = new RegExp("\\\\");
That's because first, you're writing a string literal, but you want to actually put backslashes in the resulting string, so you do that with \\ for each one backslash you want. But your regex also requires two \\ for every one real backslash you want, and so it needs to see two backslashes in the string. Hence, a total of four. This is one of the reasons I avoid using new RegExp(string) whenver I can; I get confused easily. :-)
ES2015 and ES2018 update
Fast-forward to 2015, and as Dolphin_Wood points out the new ES2015 standard gives us template literals, tag functions, and the String.raw function:
// Yes, this unlikely-looking syntax is actually valid ES2015
let str = String.raw`\apple`;
str ends up having the characters \, a, p, p, l, and e in it. Just be careful there are no ${ in your template literal, since ${ starts a substitution in a template literal. E.g.:
let foo = "bar";
let str = String.raw`\apple${foo}`;
...ends up being \applebar.
Try String.raw method:
str = String.raw`\apple` // "\apple"
Reference here: String.raw()
\ is an escape character, when followed by a non-special character it doesn't become a literal \. Instead, you have to double it \\.
console.log("\apple"); //-> "apple"
console.log("\\apple"); //-> "\apple"
There is no way to get the original, raw string definition or create a literal string without escape characters.
please try the below one it works for me and I'm getting the output with backslash
String sss="dfsdf\\dfds";
System.out.println(sss);
I have a string which i am getting
#set($locator=$dataElement.getLocator().get(0))
#set($selector = $locator.getSelector())
$selector is string type and it contains double quotes as well
when i am calling
executor.click(new Params("$selector",BY.$By));
selector have double quotes, which needs to be replaced with single quotes.
i tried with replacing but it is giving error
i referred question
Escaping quotes in velocity template
But this also don't solved my purpose
example
$selector can be something like
a[#href="somelink"]
and i want that to changed to
a[#href='someLink']
For velocity
$selector.replaceAll('"',"'")
replaces " with '
so something like:
executor.click(new Params("$selector.replaceAll('"',"'")",BY.$By));
this works fine
What is an unicode code for grave accent mark used to specify regex literal in Frege?
The character is called Acute Accent and the unicode for that is 00B4. In ubuntu, you can type that using Ctrl+Shift+u and then type 00B4 then space. However you don't really have to use that if your regex literal is more than one character in which case you can just use apostrophes.
Quoting the doc:
Regular expression literals have type Regex and are written:
´\b(foo|bar)\b´ -- string enclosed in grave accents
'\w+' -- string with length > 1 enclosed in apostrophes
The notation with the apostrophes has been introduced because many have a hard time entering a grave accent mark on their terminal. However, it is not possible to write a regular expressions with length 1 this way, because then the literal gets interpreted as Char literal. (One can write something like '(?:X)' for a Regex that matches a single 'X').
I need a complete list of characters that should be escaped in sql string parameters to prevent exceptions. I assume that I need to replace all the offending characters with the escaped version before I pass it to my ObjectDataSource filter parameter.
No, the ObjectDataSource will handle all the escaping for you. Any parametrized query will also require no escaping.
As others have pointed out, in 99% of the cases where someone thinks they need to ask this question, they are doing it wrong. Parameterization is the way to go. If you really need to escape yourself, try to find out if your DB access library offers a function for this (for example, MySQL has mysql_real_escape_string).
SQL Books online:
Search for String Literals:
String Literals
A string literal consists of zero or more characters surrounded by quotation marks. If a string contains quotation marks, these must be escaped in order for the expression to parse. Any two-byte character except \x0000 is permitted in a string, because the \x0000 character is the null terminator of a string.
Strings can include other characters that require an escape sequence. The following table lists escape sequences for string literals.
\a
Alert
\b
Backspace
\f
Form feed
\n
New line
\r
Carriage return
\t
Horizontal tab
\v
Vertical tab
\"
Quotation mark
\
Backslash
\xhhhh
Unicode character in hexadecimal notation
Here's a way I used to get rid of apostrophes. You could do the same thing with other offending characters that you run into. (example in VB.Net)
Dim companyFilter = Trim(Me.ddCompany.SelectedValue)
If (Me.ddCompany.SelectedIndex > 0) Then
filterString += String.Format("LegalName like '{0}'", companyFilter.Replace("'", "''"))
End If
Me.objectDataSource.FilterExpression = filterString
Me.displayGrid.DataBind()