Newline


Newline is a control character or sequence of control characters in a character encoding specification that is used to signify the end of a line of text and the start of a new one. Some text editors set this special character when pressing the key.
When displaying a text file, this control character causes the text editor to show the following characters in a new line.

History

In the mid-1800s, long before the advent of teleprinters and teletype machines, Morse code operators or telegraphists invented and used Morse code prosigns to encode white space text formatting in formal written text messages. In particular the Morse prosign represented by the concatenation of two literal textual Morse code "A" characters sent without the normal inter-character spacing is used in Morse code to encode and indicate a new line in a formal text message.
Later in the age of modern teleprinters standardized character set control codes were developed to aid in white space text formatting. ASCII was developed simultaneously by the International Organization for Standardization and the American Standards Association, the latter being the predecessor organization to American National Standards Institute. During the period of 1963 to 1968, the ISO draft standards supported the use of either + or alone as a newline, while the ASA drafts supported only +.
The sequence + was commonly used on many early computer systems that had adopted Teletype machines—typically a Teletype Model 33 ASR—as a console device, because this sequence was required to position those printers at the start of a new line. The separation of newline into two functions concealed the fact that the print head could not return from the far right to the beginning of the next line in time to print the next character. Any character printed after a CR would often print as a smudge in the middle of the page while the print head was still moving the carriage back to the first position. "The solution was to make the newline two characters: CR to move the carriage to column one, and LF to move the paper up." In fact, it was often necessary to send extra characters—extraneous CRs or NULs—which are ignored but give the print head time to move to the left margin. Many early video displays also required multiple character times to scroll the display.
On such systems, applications had to talk directly to the Teletype machine and follow its conventions since the concept of device drivers hiding such hardware details from the application was not yet well developed. Therefore, text was routinely composed to satisfy the needs of Teletype machines. Most minicomputer systems from DEC used this convention. CP/M also used it in order to print on the same terminals that minicomputers used. From there MS-DOS adopted CP/M's + in order to be compatible, and this convention was inherited by Microsoft's later Windows operating system.
The Multics operating system began development in 1964 and used alone as its newline. Multics used a device driver to translate this character to whatever sequence a printer needed, and the single byte was more convenient for programming. What seems like a more obvious choice——was not used, as provided the useful function of overprinting one line with another to create boldface and strikethrough effects. Perhaps more importantly, the use of alone as a line terminator had already been incorporated into drafts of the eventual ISO/IEC 646 standard. Unix followed the Multics practice, and later Unix-like systems followed Unix. This created conflicts between Windows and Unix-like OSes, whereby files composed on one OS can't be properly formatted or interpreted by another OS.

Representation

The concepts of line feed and carriage return are closely associated, and can be considered either separately or together. In the physical media of typewriters and printers, two axes of motion, "down" and "across", are needed to create a new line on the page. Although the design of a machine must consider them separately, the abstract logic of software can combine them together as one event. This is why a newline in character encoding can be defined as and combined into one.
Some character sets provide a separate newline character code. EBCDIC, for example, provides an character code in addition to the and codes. Unicode, in addition to providing the ASCII and control codes, also provides a "next line" control code, as well as control codes for "line separator" and "paragraph separator" markers.
Operating systemCharacter encodingAbbreviationhex valuedec valueEscape sequence
Unix and Unix-like systems, Multics, BeOS, Amiga, RISC OS, and othersASCII
Microsoft Windows, DOS, Atari TOS, DEC TOPS-10, RT-11, CP/M, MP/M, OS/2, Symbian OS, Palm OS, Amstrad CPC, and most other early non-Unix and non-IBM operating systemsASCII
Commodore 8-bit machines, Acorn BBC, ZX Spectrum, TRS-80, Apple II series, Oberon, the classic Mac OS, MIT Lisp Machine and OS-9ASCII
QNX pre-POSIX implementation ASCII
Acorn BBC and RISC OS spooled text output.ASCII
Atari 8-bit machinesATASCII
IBM mainframe systems, including z/OS and i5/OS EBCDIC
ZX80 and ZX81 used a specific non-ASCII character setNEWLINE

The Unicode standard defines a number of characters that conforming applications should recognize as line terminators:
This may seem overly complicated compared to an approach such as converting all line terminators to a single character, for example. However, Unicode was designed to preserve all information when converting a text file from any existing encoding to Unicode and back. Therefore, Unicode should contain characters included in existing encodings. is included in EBCDIC with code, and often mapped to, which is a control character in the C1 control set. As such, it is defined by ECMA 48, and recognized by encodings compliant with ISO/IEC 2022. C1 control set is also compatible with ISO-8859-1. The approach taken in the Unicode standard allows round-trip transformation to be information-preserving while still enabling applications to recognize all possible types of line terminators.
Recognizing and using the newline codes greater than is not often done. They are multiple bytes in UTF-8, and the code for has been used as the ellipsis character in Windows-1252. For instance:
The Unicode characters , , and are intended for presenting a user-visible character to the reader of the document, and are thus not recognized themselves as a newline.

Escape sequences

An escape sequence is a combination of characters which represents no text; instead of being displayed it is supposed to be intercepted by the program and a special function is supposed to be performed. Escape sequences are also used to handle special characters.
Special characterEscape sequenceUsed by...Examples
Perl, Vim,...Vim: \r\t/g

In programming languages

To facilitate the creation of portable programs, programming languages provide some abstractions to deal with the different types of newline sequences used in different environments.
The C programming language provides the escape sequences and . However, these are not required to be equivalent to the ASCII and control characters. The C standard only guarantees two things:
  1. Each of these escape sequences maps to a unique implementation-defined number that can be stored in a single value.
  2. When writing to a file, device node, or socket/fifo in text mode, is transparently translated to the native newline sequence used by the system, which may be longer than one character. When reading in text mode, the native newline sequence is translated back to. In binary mode, no translation is performed, and the internal representation produced by is output directly.
On Unix platforms, where C originated, the native newline sequence is ASCII , so was simply defined to be that value. With the internal and external representation being identical, the translation performed in text mode is a no-op, and Unix has no notion of text mode or binary mode. This has caused many programmers who developed their software on Unix systems simply to ignore the distinction completely, resulting in code that is not portable to different platforms.
The C library function is best avoided in binary mode because any file not written with the Unix newline convention will be misread. Also, in text mode, any file not written with the system's native newline sequence will be misread as well.
Another common problem is the use of when communicating using an Internet protocol that mandates the use of ASCII + for ending lines. Writing to a text mode stream works correctly on Windows systems, but produces only on Unix, and something completely different on more exotic systems. Using in binary mode is slightly better.
Many languages, such as C++, Perl, and Haskell provide the same interpretation of as C. C++ has an alternative I/O model where the manipulator can be used to output a newline.
Java, PHP, and Python provide the sequence. In contrast to C, these are guaranteed to represent the values and, respectively.
The Java I/O libraries do not transparently translate these into platform-dependent newline sequences on input or output. Instead, they provide functions for writing a full line that automatically add the native newline sequence, and functions for reading lines that accept any of,, or + as a line terminator. The method can be used to retrieve the underlying line separator.
Example:

String eol = System.lineSeparator;
String lineColor = "Color: Red" + eol;

Python permits "Universal Newline Support" when opening a file for reading, when importing modules, and when executing a file.
Some languages have created special variables, constants, and subroutines to facilitate newlines during program execution. In some languages such as PHP and Perl, double quotes are required to perform escape substitution for all escape sequences, including and. In PHP, to avoid portability problems, newline sequences should be issued using the PHP_EOL constant.
Example in C#:

string eol = Environment.NewLine;
string lineColor = "Color: Red" + eol;

string eol2 = "\n";
string lineColor2 = "Color: Blue" + eol2;

Issues with different newline formats

Even though the control characters are unambiguously defined in the corresponding character encoding table used by a text file, there still is an issue: there are different conventions to set and display a line break.
To denote a single line break, Unix programs use, whose hexadecimal value in ASCII is, while most programs common to MS-DOS and Microsoft Windows use +, whose hexadecimal value in ASCII is. In ASCII, carriage return is a distinct control character.
The different newline conventions cause text files that have been transferred between systems of different types to be displayed incorrectly.
Text in files created with programs which are common on Unix-like or classic Mac OS, appear as a single long line on most programs common to MS-DOS and Microsoft Windows because these do not display a single or a single as a line break.
Conversely, when viewing a file originating from a Windows computer on a Unix-like system, the extra may be displayed as a second line break, as, or as at the end of each line.
Furthermore, programs other than text editors may not accept a file, e.g. some configuration file, encoded using the foreign newline convention, as a valid file.
The problem can be hard to spot because some programs handle the foreign newlines properly while others do not. For example, a compiler may fail with obscure syntax errors even though the source file looks correct when displayed on the console or in an editor. On a Unix-like system, the command will send the file to stdout and make the visible, which can be useful for debugging. Modern text editors generally recognize all flavours of + newlines and allow users to convert between the different standards. Web browsers are usually also capable of displaying text files and websites which use different types of newlines.
Even if a program supports different newline conventions, these features are often not sufficiently labeled, described, or documented. Typically a menu or combo-box enumerating different newline conventions will be displayed to users without an indication if the selection will re-interpret, temporarily convert, or permanently convert the newlines. Some programs will implicitly convert on open, copy, paste, or save—often inconsistently.
Most textual Internet protocols mandate the use of ASCII + on the protocol level, but recommend that tolerant applications recognize lone as well. Despite the dictated standard, many applications erroneously use the C newline escape sequence instead of the correct combination of carriage return escape and newline escape sequences . This accidental use of the wrong escape sequences leads to problems when trying to communicate with systems adhering to the stricter interpretation of the standards instead of the suggested tolerant interpretation. One such intolerant system is the qmail mail transfer agent that actively refuses to accept messages from systems that send bare instead of the required +.
The standard Internet Message Format for eMail states: CR and LF MUST only occur together as CRLF; they MUST NOT appear independently in the body.
The File Transfer Protocol can automatically convert newlines in files being transferred between systems with different newline representations when the transfer is done in "ASCII mode". However, transferring binary files in this mode usually has disastrous results: any occurrence of the newline byte sequence—which does not have line terminator semantics in this context, but is just part of a normal sequence of bytes—will be translated to whatever newline representation the other system uses, effectively corrupting the file. FTP clients often employ some heuristics to automatically select either binary or ASCII mode, but in the end it is up to users to make sure their files are transferred in the correct mode. If there is any doubt as to the correct mode, binary mode should be used, as then no files will be altered by FTP, though they may display incorrectly.

Conversion between newline formats

s are often used for converting a text file between different newline formats; most modern editors can read and write files using at least the different ASCII / conventions.
For example, the editor Vim can make a file compatible with the Windows Notepad text editor. Within vim

:set fileformat=dos
:wq

Editors can be unsuitable for converting larger files or bulk conversion of many files. For larger files the following command is often used:

D:\>TYPE unix_file | FIND /V "" > dos_file

Special purpose programs to convert files between different newline conventions include, and, and, and.
The command is available on virtually every Unix-like system and can be used to perform arbitrary replacement operations on single characters. A DOS/Windows text file can be converted to Unix format by simply removing all ASCII characters with
$ tr -d '\r' < inputfile > outputfile
or, if the text has only newlines, by converting all newlines to with
$ tr '\r' '\n' < inputfile > outputfile
The same tasks are sometimes performed with awk, sed, or in Perl if the platform has a Perl interpreter:

$ awk inputfile > outputfile # UNIX to DOS
$ awk inputfile > outputfile # DOS to UNIX
$ sed -e 's/$/\r/' inputfile > outputfile # UNIX to DOS
$ sed -e 's/\r$//' inputfile > outputfile # DOS to UNIX
$ perl -pe 's/\r?\n|\r/\r\n/g' inputfile > outputfile # Convert to DOS
$ perl -pe 's/\r?\n|\r/\n/g' inputfile > outputfile # Convert to UNIX
$ perl -pe 's/\r?\n|\r/\r/g' inputfile > outputfile # Convert to old Mac

The command can identify the type of line endings:

$ file myfile.txt
myfile.txt: ASCII English text, with CRLF line terminators

The Unix egrep command can be used to print filenames of Unix or DOS files :

$ egrep -L '\r\n' myfile.txt # show UNIX style file
$ egrep -l '\r\n' myfile.txt # show DOS style file

Other tools permit the user to visualise the EOL characters:

$ od -a myfile.txt
$ cat -e myfile.txt
$ hexdump -c myfile.txt

Interpretation

Two ways to view newlines, both of which are self-consistent, are that newlines either separate lines or that they terminate lines. If a newline is considered a separator, there will be no newline after the last line of a file. Some programs have problems processing the last line of a file if it is not terminated by a newline. On the other hand, programs that expect newline to be used as a separator will interpret a final newline as starting a new line. Conversely, if a newline is considered a terminator, all text lines including the last are expected to be terminated by a newline. If the final character sequence in a text file is not a newline, the final line of the file may be considered to be an improper or incomplete text line, or the file may be considered to be improperly truncated.
In text intended primarily to be read by humans using software which implements the word wrap feature, a newline character typically only needs to be stored if a line break is required independent of whether the next word would fit on the same line, such as between paragraphs and in vertical lists. Therefore, in the logic of word processing and most text editors, newline is used as a paragraph break and is known as a "hard return", in contrast to "soft returns" which are dynamically created to implement word wrapping and are changeable with each display instance. In many applications a separate control character called "manual line break" exists for forcing line breaks inside a single paragraph. The glyph for the control character for a hard return is usually a pilcrow, and for the manual line break is usually a carriage return arrow.

Reverse and partial line feeds

, is used to move the printing position back one line so that other characters may be printed over existing text. This may be done to make them bolder, or to add underlines, strike-throughs or other characters such as diacritics.
Similarly, and can be used to advance or reverse the text printing position by some fraction of the vertical line spacing. These can be used in combination for subscripts and superscripts, and may also be useful for printing diacritics.
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