Backslash

The backslash \ is a special symbol used mostly in computing and mathematics. It looks like the mirror image of the common slash ( / ), which is why it is sometimes called a reverse slash. Even though we use slashes all the time, the backslash is a newer symbol, first appearing in writing during the 1930s.

People have used many fun names for the backslash, like "hack," "whack," "slosh," or "backslant." In computer languages like C and UNIX, it is often called the "escape" character because it helps control special actions in coding.

Even though it looks simple, the backslash plays an important role in many computer systems and programs. It helps tell computers where files are stored and how to handle special symbols in code.

History

The backslash was first shown in a 1937 manual from the Teletype Corporation, which had a picture of a special keyboard. In 1945, Teletype called it the “diagonal key.”

Later, in 1960, IBM added the backslash to its character set. In 1961, an IBM employee suggested including it in a new standard, calling it a “reverse division operator.” This helped programmers use certain symbols in early computer languages.

Usage

In many programming languages such as C, Perl, PHP, Python, and Unix scripting languages, the backslash is used as an escape character. This means it changes how the next character is seen. For example, in C, \n makes a new line, and \" shows a real double quote.

In regular expression languages, the backslash changes normal characters into special ones and vice versa. For example, \||b looks for either '|' or 'b'.

In Visual Basic and some other BASIC languages, the backslash is used to show integer division.

In APL, the backslash has special meanings when used with arrays.

In PHP version 5.3 and higher, the backslash shows a namespace.

In Haskell, the backslash introduces special characters and lambda functions.

In MS-DOS and Microsoft Windows, the backslash is used in filenames to separate folders.

The backslash is also used in TeX typesetting and RTF files to start special formatting.

In mathematics, the backslash can show the difference between sets.

In MATLAB and GNU Octave, the backslash is used for a special kind of matrix divide.

Confusion with ¥ and other characters

In some computer systems used in Japan, the symbol that looks like a backslash is shown as a yen sign (¥) instead. This happens because these systems use a different set of symbols, and the place where the backslash should appear shows the yen sign. This can be confusing, especially when looking at old computer files.

Other countries also had similar issues, where the backslash looked like different symbols, such as ₩ in Korea, Ö in Germany and Sweden, Ø in Denmark and Norway, ç in France, and Ñ in Spain. Today, these problems are less common, but some older systems can still cause this mix-up.

In 1991, a suggestion was made to use // instead of a backslash in internet standards to avoid confusion. You might see this in some older internet documents.

Unicode

Unicode includes several special symbols that look like the backslash. These symbols have unique codes that tell computers how to show them. Some examples are the regular backslash, a bigger version, and a box shape that goes from the top left to the bottom right.