For example, if you have escaped string like
Hello wo\\\\rld.txt
you want to unescape it and make it, Hello wo\\rld.txt
essentially making,
\\ -> \, \\r -> \r, \\n -> \n,
etc
I tried doing string replace like:
out = out.replace("\\", "\");
but that is syntax error
You still have to escape every \ in your string literals i.e. out = out.replace("\\\\", "\\");
Related
I want to replace \n with a space in a String with a recursive function using pattern matching, but I can't figure out how to match the \ char.
This is my function:
replace :: String -> String
replace ('\\':'n':xs) = ' ' : replace xs
replace (x:xs) = x : replace xs
replace "" = ""
In ('\':'n':xs) the backslash would escape the single quote and mess up the code, so I wrote ('\\':'n':xs) expecting that the first \ would escape the escape of the second \ and would match a backslash in a String. However, it doesn't.
This is what happens when I try the function in GHCi:
*Example> replace "m\nop"
"m\nop"
*Example> replace "m\\nop"
"m op"
How can I match a single backslash?
\n is a single character. If we use \n in a string like "Hello\nWorld!", then the resulting list looks like this: ['H','e','l','l','o','\n','W','o','r','l','d','!']. \n denotes a newline character, a single ASCII byte 10. However, since a newline isn't really easy to type in many programming languages, the escape sequence \n is used instead in string literals.
If you want to pattern match on a newline, you must use the whole escape sequence:
replace :: String -> String
replace ('\n':xs) = ' ' : replace xs
replace (x:xs) = x : replace xs
replace "" = ""
Otherwise, you will only match the literal \.
Exercise: Now that replace works, try to use map instead of explicit recursion.
I am trying to make a string variable containing :
"C:\Program Files\Sublime Text 3\sublime_text.exe" C:\Users\User\Desktop\Guess.py
Unfortunately I am not succeeding in doing so. Is there a way to put the text about as is into a variable, double quotes and all?
In your example string you have characters that need escaping: " and \
fmt.Println("\"C:\\Program Files\\Sublime Text 3\\sublime_text.exe\" C:\\Users\\User\\Desktop\\Guess.py")
You can also use back quotes to create what is called a raw string which doesn't require escaping those characters.
fmt.Println(`"C:\Program Files\Sublime Text 3\sublime_text.exe" C:\Users\User\Desktop\Guess.py`)
List of escapes:
\a U+0007 alert or bell
\b U+0008 backspace
\f U+000C form feed
\n U+000A line feed or newline
\r U+000D carriage return
\t U+0009 horizontal tab
\v U+000b vertical tab
\\ U+005c backslash
\' U+0027 single quote (valid escape only within rune literals)
\" U+0022 double quote (valid escape only within string literals)
See the official docs.
In perl suppose I have a string like 'hello\tworld\n', and what I want is:
'hello world
'
That is, "hello", then a literal tab character, then "world", then a literal newline. Or equivalently, "hello\tworld\n" (note the double quotes).
In other words, is there a function for taking a string with escape sequences and returning an equivalent string with all the escape sequences interpolated? I don't want to interpolate variables or anything else, just escape sequences like \x, where x is a letter.
Sounds like a problem that someone else would have solved already. I've never used the module, but it looks useful:
use String::Escape qw(unbackslash);
my $s = unbackslash('hello\tworld\n');
You can do it with 'eval':
my $string = 'hello\tworld\n';
my $decoded_string = eval "\"$string\"";
Note that there are security issues tied to that approach if you don't have 100% control of the input string.
Edit: If you want to ONLY interpolate \x substitutions (and not the general case of 'anything Perl would interpolate in a quoted string') you could do this:
my $string = 'hello\tworld\n';
$string =~ s#([^\\A-Za-z_0-9])#\\$1#gs;
my $decoded_string = eval "\"$string\"";
That does almost the same thing as quotemeta - but exempts '\' characters from being escaped.
Edit2: This still isn't 100% safe because if the last character is a '\' - it will 'leak' past the end of the string though...
Personally, if I wanted to be 100% safe I would make a hash with the subs I specifically wanted and use a regex substitution instead of an eval:
my %sub_strings = (
'\n' => "\n",
'\t' => "\t",
'\r' => "\r",
);
$string =~ s/(\\n|\\t|\\n)/$sub_strings{$1}/gs;
When i am trying to read data from the excel file it giving me error as "Invalid escape sequence (valid ones are \b \t \n \f \r \" \' \ )"
How to resolve this??
My string is
String path = "C:\Documents and Settings\Desktop\Param.xlsx";
I have tried both the way but couldn't able to run my script.
I 'm writing java program to read data from the excel file. so for path i used that string but unable to make it happen!
Please help me.
Try this one:
int i=0;
StringTokenizer strToken = new StringTokenizer(path, "\\");
while (strToken.hasMoreTokens()) {
i += 1;
System.out.println(i + ". element: " + strToken.nextToken());
}
You have not provided so much information so I am trying to guess what you are actually doing. But assuming that you want to open an Excel file in C# then your string is wrong because it contains invalid escape sequences. However, that is easily fixed:
String path = #"C:\Documents and Settings\Desktop\Param.xlsx";
Notice the # in front of the string.
Or you could escape the backslashes in the string:
String path = "C:\\Documents and Settings\\Desktop\\Param.xlsx";
I have an assignment to create a lexical analyser and I've got everything working except for one bit.
I need to create a string that will accept a new line, and the string is delimited by double quotes.
The string accepts any number, letter, some specified punctuation, backslashes and double quotes within the delimiters.
I can't seem to figure out how to escape a new line character.
Is there a certain way of escaping characters like new line and tab?
Here's some of my code that might help
< STRING : ( < QUOTE> (< QUOTE > | < BACKSLASH > | < ID > | < NUM > | " " )* <QUOTE>) >
< #QUOTE : "\"" >
< #BACKSLASH : "\\" >
So my string should allow for a quote, then any of the following characters like a backslash, a whitespace, a number etc, and then followed by another quote.
The newline char like "\n" is what's not working.
Thanks in advance!
For string literals, JavaCC borrows the syntax of Java. So, a single-character literal comprising a carriage return is escaped as "\r", and a single-character literal comprising a line feed is escaped as "\n".
However, the processed string value is just a single character; it is not the escape itself. So, suppose you define a token for line feed:
< LF : "\n" >
A match of the token <LF> will be a single line-feed character. When substituting the token in the definition of another token, the single character is effectively substituted. So, suppose you have the higher-level definition:
< STRING : "\"" ( <LF> ) "\"" >
A match of the token <STRING> will be three characters: a quotation mark, followed by a line feed, followed by a quotation mark. What you seem to want instead is for the escape sequence to be recognized:
< STRING : "\"" ( "\\n" ) "\"" >
Now a match of the token <STRING> will be four characters: a quotation mark, followed by an escape sequence representing a line feed, followed by a quotation mark.
In your current definition, I see that other often-escaped metacharacters like quotation mark and backslash are also being recognized literally, rather than as escape sequences.