I know that file line separaters are very different under certain operating systems, for windows it's CRLF, under linux is LF, and under MacOS is CR. But who on earth named those ascii characters? Are those (LF and CR etc.) abbreviation or something else? And dose every ascii character have a name like this?
CR stands for Carriage Return, LF stands for Line Feed. These names come from the age of typewriters. In order to start writing on the next line, you would push your carriage (the moving part of the typewriter) all the way back to the left, then engage the feed lever to pull the paper one line up.
And yes, other "control characters" have names like those too. See here: http://en.wikipedia.org/wiki/ASCII#ASCII_control_characters
CR stands for "carriage return", which means the returning of the typewriters head to the start of the line. LF is for "line feed" which advances the sheet of paper in the typewriter to the next line.
In most typewriters, CR and LF could be triggered by a single mechanism, but sometimes you also had an additional line feed key to quickly advance to the next line without moving the head (useful for formulars). And you could also omit the LF action on CR in order to write to a given line more than once.
Related
Has anyone any idea why the following would format itself in a weird way? In several years I've had no problem with creating simple text output but this problem has me baffled.
I'm using the line
print "$BC,$Ttl,$FN,$SN,$Finalage,$OurLoc,$OurDT,$FinalPC\n";
Every value is a simple text string on which I've run "chomp" to remove return characters.
I would expect the output to look like the following:
*DD10099999,,Information Services,Guest Ticket 2,41,C G,03/11/2020,NE8 9BB*
$BC is the first item and $FinalPC is the postcode at the end.
Instead I get:
*,NE8 9BB99, ,Information Services,Guest Ticket 2,41,C G,03/11/2020*
The final item has somehow moved to the beginning of the line and overwritten the first item. This is happening consistently on every line of my screen and text file output and I'm completely stumped as to why. The data is read from a text file and compared with database output which is also simple text. There are no occurrences of \b anywhere in my code. Why would a backspace character get into it?
The string in $OurDT ends with a carriage return, which causes your terminal to home the cursor. Presumably, the value of $OurDT came from a Windows file read on a unixy machine.
One option is to fix the file (e.g. by using the dos2unix utility).
Another is to accept both CRLF and LF as line endings (e.g. by using s/\s+\z// instead of chomp).
So this web page is rendering with these symbols and they are found throughout this website/application but on no other sites. Can anyone tell me
What this symbol is?
Why it is showing up only in one browser?
That character is U+2028 Line Separator, which is a kind of newline character. Think of it as the Unicode equivalent of HTML’s <br>.
As to why it shows up here: my guess would be that an internal database uses LSEP to not conflict with literal newlines or HTML tags (which might break the database or cause security errors), and either:
The server-side scripts that convert the database to HTML neglected to replace LSEP with <br>
Chrome just breaks standards by displaying LSEP as a printing (visible) character, or
You have a font installed that displays LSEP as a printing character that only Chrome detects. To figure out which font it is, right click on the offending text and click “Inspect”, then switch to the “Computed” tab on the right-hand panel. At the very bottom you should see a section labeled “Rendered Fonts” which will help you locate the offending font.
More information on the line separator, excerpted from the Unicode standard, Chapter 5.8, Newline Guidelines (on p. 12 of this PDF):
Line Separator and Paragraph Separator
A paragraph separator—independent of how it is encoded—is used to indicate a
separation between paragraphs. A line separator indicates where a line break
alone should occur, typically within a paragraph. For example:
This is a paragraph with a line separator at this point,
causing the word “causing” to appear on a different line, but not causing
the typical paragraph indentation, sentence breaking, line spacing, or
change in flush (right, center, or left paragraphs).
For comparison, line separators basically correspond to HTML <BR>, and
paragraph separators to older usage of HTML <P> (modern HTML delimits
paragraphs by enclosing them in <P>...</P>). In word processors, paragraph
separators are usually entered using a keyboard RETURN or ENTER; line
separators are usually entered using a modified RETURN or ENTER, such as
SHIFT-ENTER.
A record separator is used to separate records. For example, when exchanging
tabular data, a common format is to tab-separate the cells and to use a CRLF
at the end of a line of cells. This function is not precisely the same as line
separation, but the same characters are often used.
Traditionally, NLF started out as a line separator (and sometimes record
separator). It is still used as a line separator in simple text editors such as
program editors. As platforms and programs started to handle word processing
with automatic line-wrap, these characters were reinterpreted to stand for
paragraph separators. For example, even such simple programs as the Windows
Notepad program and the Mac SimpleText program interpret their platform’s NLF
as a paragraph separator, not a line separator. Once NLF was reinterpreted to
stand for a paragraph separator, in some cases another control character was
pressed into service as a line separator. For example, vertical tabulation VT
is used in Microsoft Word. However, the choice of character for line separator
is even less standardized than the choice of character for NLF. Many Internet
protocols and a lot of existing text treat NLF as a line separator, so an
implementer cannot simply treat NLF as a paragraph separator in all
circumstances.
Further reading:
Unicode Technical Report #13: Newline Guidelines
General Punctuation (U+2000–U+206F) chart PDF
SE: Why are there so many spaces and line breaks in Unicode?
SO: What is unicode character 2028 (LS / Line Separator) used for?
U+2028 on codepoints.net A misprint here says that U+2028 was added in v. 1.1 of the Unicode standard, which is false — it was added in 1.0
I found that in WordPress the easiest way to remove "L SEP" and "P SEP" characters is to execute this two SQL queries:
UPDATE wp_posts SET post_content = REPLACE(post_content, UNHEX('e280a9'), '')
UPDATE wp_posts SET post_content = REPLACE(post_content, UNHEX('e280a8'), '')
The javascript way (mentioned in some of the answers) can break some things (in my case some modal windows stopped working).
You can use this tool...
http://www.nousphere.net/cleanspecial.php
...to remove all the special characters that Chrome displays.
Steps:
Paste your HTML and Clean using HTML option.
You can manually delete the characters in the editor on this page and see the result.
Paste back your HTML in file and save :)
I recently ran into this issue, tried a number of fixes but ultimately I had to paste the text into VIM and there was an extra space I had to delete. I tried a number of HTML cleaners but none of them worked, VIM was the key!
9999years answers is great.
In case you use Symfony with Twig template I would recommend to check for an empty Twig block. In my case it was an empty Twig block with an invisible char inside.
The LSEP char was only displayed on certain device / browser.
On the other I had a blank space above the header and I could not see any invisible char.
I had to inspect the GET request to see that the value 1f18 was before the open html tag.
Once I removed an empty Twig block it was gone.
hope this can help someone one day ...
My problem was similar, it was "PSEP" or "P SEP". Similar issue, an invisible character in my file.
I replaced \x{2029} with a normal space. Fixed. This problem only appeared on Windows Chrome. Not on my Mac.
I agree with #Kapil Bathija - Basically you can copy & paste your HTML code into http://www.nousphere.net/cleanspecial.php and convert it.
Then it will convert the special characters for you - Just remove the spaces in between the words and you will realize you have to press backspace 2x meaning there is an invalid character that can't be translated.
I had the same issue and it worked just fine afterwards.
You can also copy the text, paste it into a HTML editor such as Coda, remove the linebreak, copy it and paste it back into your site.
Video here: https://www.loom.com/share/501498afa7594d95a18382f1188f33ce
Looks like my client pasted HTML into Wordpress after initially creating it with MS-Word. Even deleting the and visible spaces did not fix the issue. The extended characters became visible in vi/vim.
If you don't have vi/vim available, try highlighting from 2 chars before the LSEP to 2 chars after the LSEP; delete that chunk, and re-type the correct characters.
I used http://icalvalid.cloudapp.net/Default.aspx link to validate the link of my calendar. And i got the warning "Line endings must be a Carriage Return/Line Feed (CRLF) pair.". What does this mean? What do I need to this to remove this warning. Can anyone please help me on this issues.
Your help will be appreciated. Thanks.
It means the file has to be in "Windows" format, rather than UNIX format. If you're creating the file from code, it means that you need to write "\r\n" at the end of the lines, rather than just "\n" -- assuming you're using some language where that makes sense, of course. If you're creating the file by hand, save it in "DOS mode" from your editor.
It seems you are running a Linux or Mac OS X box, which uses just the LF (line feed) ASCII value for line endings.
Windows uses CRLF (carriage return; line feed) for line endings.
You must convert this, for example with Notepad++ (though dedicated application exist).
tr -d '\r' < userlist.txt > newlist.txt
This question already has answers here:
Closed 12 years ago.
Possible Duplicate:
What is the difference between \r and \n?
Hi,
What is difference between \n (newline) and \r (carriage return)? They both move current cursor to the next line. Are they same?
\r returns the cursor to the beginning of the line, NOT to the next line. When you use \nin Linux, \r is implied, in windows, it is not.
Using \r in Unix-like systems may result in overwriting the same line.
I suggest you read this.
In short, a newline in Windows is "\r\n", while a newline in Unix is just "\n" (and, just to make life difficult, a newline in older Macs is "\r")
Actually, a carriage return is supposed to move the cursor to the beginning of the current line. Then, newline moves the cursor exactly down one.
Nowadays, compilers will often automatically convert one or the other to \r\n on Windows or \n on Linux. Mac used to use \r but they have changed to the \n convention.
(edit: removed false/untested statements)
Read The Great Newline Schism it explains everything in deep detail with great humor.
Ah the old days of the typewriter...
The difference between the two stems from days of yonder when typing was done directly to paper. It required two actions to go to the next line:
pushing the 'carriage' (big cilinder on the top) back to the left (this is where the character would end up).
shifting the paper one line up. (thus going down one line)
Splitting these two actions facilitated going back to a precise character position to correct it (there was no way to go up one line, or left one character!). Holding paper whiteout on the erroneous character and hitting that key would neatly whiteout exactly that erroneous character, then you could go back again and hit the correct key
(there was a key for not moving the carriage though).
In the young computer age these actions were translated 1 to 1 into \r for carriage return and \n for shifting the 'paper'.
Nowadays the major operating systems apparently have differing opinions on whether this is still necessary for computer technology where going back to previous position is much easier. However, in modern programming languages you'll generally see that \n is assumed to mean \r\n.
No they're not. Modern text editors often treat them the same however because their old uses don't make much sense for digital word processors.
For example \r literally means "return to the beginning of the line". While this might have been useful for a typewriter if you just wanted to overwrite everything on that line this sort of functionality doesn't make much sense for digital type.
\n on the other hand would simply move down a line without returning to the beginning. This was also useful on a typewriter for indentation or bulleting. Again, not something that makes much sense for digital type.
Telnet is one example where both characters are still used in this manner.
Both characters were included in ascii language simply because when it was being spec'd they hadn't realized that functionality that was useful on a typewriter didn't make much sense on a computer.
How are \r and \n different? I think it has something to do with Unix vs. Windows vs. Mac, but I'm not sure exactly how they're different, and which to search for/match in regexes.
They're different characters. \r is carriage return, and \n is line feed.
On "old" printers, \r sent the print head back to the start of the line, and \n advanced the paper by one line. Both were therefore necessary to start printing on the next line.
Obviously that's somewhat irrelevant now, although depending on the console you may still be able to use \r to move to the start of the line and overwrite the existing text.
More importantly, Unix tends to use \n as a line separator; Windows tends to use \r\n as a line separator and Macs (up to OS 9) used to use \r as the line separator. (Mac OS X is Unix-y, so uses \n instead; there may be some compatibility situations where \r is used instead though.)
For more information, see the Wikipedia newline article.
EDIT: This is language-sensitive. In C# and Java, for example, \n always means Unicode U+000A, which is defined as line feed. In C and C++ the water is somewhat muddier, as the meaning is platform-specific. See comments for details.
In C and C++, \n is a concept, \r is a character, and \r\n is (almost always) a portability bug.
Think of an old teletype. The print head is positioned on some line and in some column. When you send a printable character to the teletype, it prints the character at the current position and moves the head to the next column. (This is conceptually the same as a typewriter, except that typewriters typically moved the paper with respect to the print head.)
When you wanted to finish the current line and start on the next line, you had to do two separate steps:
move the print head back to the beginning of the line, then
move it down to the next line.
ASCII encodes these actions as two distinct control characters:
\x0D (CR) moves the print head back to the beginning of the line. (Unicode encodes this as U+000D CARRIAGE RETURN.)
\x0A (LF) moves the print head down to the next line. (Unicode encodes this as U+000A LINE FEED.)
In the days of teletypes and early technology printers, people actually took advantage of the fact that these were two separate operations. By sending a CR without following it by a LF, you could print over the line you already printed. This allowed effects like accents, bold type, and underlining. Some systems overprinted several times to prevent passwords from being visible in hardcopy. On early serial CRT terminals, CR was one of the ways to control the cursor position in order to update text already on the screen.
But most of the time, you actually just wanted to go to the next line. Rather than requiring the pair of control characters, some systems allowed just one or the other. For example:
Unix variants (including modern versions of Mac) use just a LF character to indicate a newline.
Old (pre-OSX) Macintosh files used just a CR character to indicate a newline.
VMS, CP/M, DOS, Windows, and many network protocols still expect both: CR LF.
Old IBM systems that used EBCDIC standardized on NL--a character that doesn't even exist in the ASCII character set. In Unicode, NL is U+0085 NEXT LINE, but the actual EBCDIC value is 0x15.
Why did different systems choose different methods? Simply because there was no universal standard. Where your keyboard probably says "Enter", older keyboards used to say "Return", which was short for Carriage Return. In fact, on a serial terminal, pressing Return actually sends the CR character. If you were writing a text editor, it would be tempting to just use that character as it came in from the terminal. Perhaps that's why the older Macs used just CR.
Now that we have standards, there are more ways to represent line breaks. Although extremely rare in the wild, Unicode has new characters like:
U+2028 LINE SEPARATOR
U+2029 PARAGRAPH SEPARATOR
Even before Unicode came along, programmers wanted simple ways to represent some of the most useful control codes without worrying about the underlying character set. C has several escape sequences for representing control codes:
\a (for alert) which rings the teletype bell or makes the terminal beep
\f (for form feed) which moves to the beginning of the next page
\t (for tab) which moves the print head to the next horizontal tab position
(This list is intentionally incomplete.)
This mapping happens at compile-time--the compiler sees \a and puts whatever magic value is used to ring the bell.
Notice that most of these mnemonics have direct correlations to ASCII control codes. For example, \a would map to 0x07 BEL. A compiler could be written for a system that used something other than ASCII for the host character set (e.g., EBCDIC). Most of the control codes that had specific mnemonics could be mapped to control codes in other character sets.
Huzzah! Portability!
Well, almost. In C, I could write printf("\aHello, World!"); which rings the bell (or beeps) and outputs a message. But if I wanted to then print something on the next line, I'd still need to know what the host platform requires to move to the next line of output. CR LF? CR? LF? NL? Something else? So much for portability.
C has two modes for I/O: binary and text. In binary mode, whatever data is sent gets transmitted as-is. But in text mode, there's a run-time translation that converts a special character to whatever the host platform needs for a new line (and vice versa).
Great, so what's the special character?
Well, that's implementation dependent, too, but there's an implementation-independent way to specify it: \n. It's typically called the "newline character".
This is a subtle but important point: \n is mapped at compile time to an implementation-defined character value which (in text mode) is then mapped again at run time to the actual character (or sequence of characters) required by the underlying platform to move to the next line.
\n is different than all the other backslash literals because there are two mappings involved. This two-step mapping makes \n significantly different than even \r, which is simply a compile-time mapping to CR (or the most similar control code in whatever the underlying character set is).
This trips up many C and C++ programmers. If you were to poll 100 of them, at least 99 will tell you that \n means line feed. This is not entirely true. Most (perhaps all) C and C++ implementations use LF as the magic intermediate value for \n, but that's an implementation detail. It's feasible for a compiler to use a different value. In fact, if the host character set is not a superset of ASCII (e.g., if it's EBCDIC), then \n will almost certainly not be LF.
So, in C and C++:
\r is literally a carriage return.
\n is a magic value that gets translated (in text mode) at run-time to/from the host platform's newline semantics.
\r\n is almost always a portability bug. In text mode, this gets translated to CR followed by the platform's newline sequence--probably not what's intended. In binary mode, this gets translated to CR followed by some magic value that might not be LF--possibly not what's intended.
\x0A is the most portable way to indicate an ASCII LF, but you only want to do that in binary mode. Most text-mode implementations will treat that like \n.
"\r" => Return
"\n" => Newline or Linefeed
(semantics)
Unix based systems use just a "\n" to end a line of text.
Dos uses "\r\n" to end a line of text.
Some other machines used just a "\r". (Commodore, Apple II, Mac OS prior to OS X, etc..)
\r is used to point to the start of a line and can replace the text from there, e.g.
main()
{
printf("\nab");
printf("\bsi");
printf("\rha");
}
Produces this output:
hai
\n is for new line.
In short \r has ASCII value 13 (CR) and \n has ASCII value 10 (LF).
Mac uses CR as line delimiter (at least, it did before, I am not sure for modern macs), *nix uses LF and Windows uses both (CRLF).
In addition to #Jon Skeet's answer:
Traditionally Windows has used \r\n, Unix \n and Mac \r, however newer Macs use \n as they're unix based.
\r is Carriage Return; \n is New Line (Line Feed) ... depends on the OS as to what each means. Read this article for more on the difference between '\n' and '\r\n' ... in C.
in C# I found they use \r\n in a string.
\r used for carriage return. (ASCII value is 13)
\n used for new line. (ASCII value is 10)