Backslash

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The backslash ( \ ) is a typography mark (glyph) used primarily in computing and is a mirror image of a common slash (/). Sometimes called hack , whacked , escaped (from C/UNIX), backslash , slash , downwhack , backslant , backwhack , bash , b>, and reversed virgule . In Unicode, it is encoded on U 005C \ REVERSE SOLIDUS (HTMLÃ, & amp; # 92 ; ).

Video Backslash

History

Bob Bemer introduced the \ character to ASCII on September 18, 1961, as a result of a character-frequency study. Specifically, \ is introduced so the boolean operator ALGOL ? (AND) and ? (OR) can be composed in ASCII as /\ and \/ respectively. Both operators are included in an early version of the C programming language that is included with Unix V6, Unix V7 and more currently BSD 2.11.

Maps Backslash

Usage

In many programming languages ​​such as C, Perl, PHP, Python and in Unix scripting languages, backslashes are used as escape characters, to indicate that the characters following them should be specially treated (otherwise will be treated normally), or usually (if it will be treated in particular). For example in the quoted C string, the sequence \ n produces a new line byte instead of 'n', and the order of \ " produces an actual double quote rather than the special meaning of the terminating double quote string. In different languages ​​regular expressions are used in this way, converting subsequent literal characters into metacharacters and vice versa. After this use, the double backslash sequence \\ produces a normal backslash literally.

The ALGOL 68 programming language uses "\" as its Desymed Exponential Symbol. ALGOL 68 has a choice of 4 Decimal Expectation Symbols: e, E, \, or ₁₀ . Example: 6.0221415e23 , 6.0221415E23 , < code lang = "ALGOL"> 6.0221415 \ 23 or 6.0221415 10 23 .

Backslash is used in TeX typesetting systems and in RTF files to start markup tags. In Haskell, backslash is used both for introducing special characters and for introducing lambda functionality (since it is a reasonable estimate in ASCII from the Greek lambda letter ,?).

MS-DOS 2.0, released in 1983, copied the hierarchical file system of Unix and thus used (front) the slash, but (possibly at IBM's insistence) added a backslash to allow the path to be typed at the command line interpreter prompt while maintaining compatibility with MS- DOS 1.0 and CP/M where the slash is a command line option indicator (typing " DIR/W " gives "width" options to " DIR " command, so some methods another is required if you really want to run a program called W in a directory named DIR ). Except for COMMAND.COM, all other parts of the operating system accept both characters in the path, but the Microsoft convention keeps the backslash, and the back API uses backslashes. This applies to MS-DOS and PC DOS, but also to all other DOS operating systems such as DR-DOS, PTS-DOS, RxDOS or FreeDOS as well as for Concurrent DOS, Multiuser DOS, FlexOS, 4680 OS, 4690 OS, OS/2 and Windows. In some DOS versions, the option characters can be changed from / to - via SWITCHAR, which allows COMMAND.COM to retain / in the command name.

The Microsoft Windows family of operating systems inherits MS-DOS behavior and still supports good characters - but individual Windows programs and sub-systems may, incorrectly, only accept backslashes as path separators, or may misinterpret slashes if used that way. Some programs will only accept slashes if the path is placed in double quotes. Failure of Microsoft's security features to recognize unexpected slashes in the local path and the Internet, while other parts of the operating system still act upon them, has caused some serious deviations in security. Resources that should not be available have been accessed with paths using certain mixes, such as http://example.net/secure\private.aspx .

In mathematics, a slash-like symbol is used for the specified difference. Backslash is also sometimes used to indicate the right coset space.

In some dialects of the BASIC programming language, backslashes are used as operator symbols to indicate integer division.

In MATLAB and GNU Octave, the backslash is used to divide the left matrix, while the slash is to divide the exact matrix.

In PHP 5.3 and higher versions, the backslash is used to indicate the namespace.

In USFM, backslash is used to mark the format feature for editing Bible translations.

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Confusion in use

In the Japanese encoding of ISO 646 (7-bit code based on ASCII), JIS X 0201 (8-bit code), and Shift JIS (8-bit multi-byte coding for ASCII), the code point 0x5C will be used for backslash in ASCII is instead given as a sign of the yen ( ¥  ¥), while in Korean encoding, it is withdrawn as a symbol of the won currency (?). Computer programs still treat the code as a backslash in this environment, causing confusion, especially in MS-DOS file names. Due to the extensive use of the backslash code dot to represent the yen mark, even now some Unicode fonts like MS Mincho create a backslash character as  ¥, so Unicode 00A5 ( ¥  ¥) and 005C (\) characters look identical currently selected fonts. Several other ISO 646 versions also replaced backslashes with characters such as ÃÆ'â € "(Germany, Sweden), ÃÆ'ËÅ" (Denmark, Norway), ÃÆ'§ (France) and ÃÆ'â € ~ (Spain), leading to similar problems. Since the initial characters are not available in all character sets and keyboard layouts, ANSI C can transcribe them in trigraph ??/ which, even in literal strings, is equivalent to \ characters. RFC 1345 recommends to write the character as digraph //, if it is not available.

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References

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External links

• Bob Bemer. "How ASCII gets its backslash". Archived from the original in 2013-07-19.
• Definition of Backslash by Linux Information Project (LINFO)

Source of the article : Wikipedia