How to type Backslash
\ is the key above Enter on a US keyboard and the extra key left of Z on a UK one. Press the key above Enter on a UK keyboard and you get # instead, which is the whole of why the key looks wrong: nothing is broken and the layout is simply the other one. Alt + 92 on the numeric keypad produces it on any Windows layout, which is the way in when the keyboard in front of you has no key for it, and \ writes it in HTML. Its codepoint is U+005C.
Reverse Solidus
- Copy it
- Unicode
- U+005C
- Windows
- Alt + 92
| Where | Shortcut | How |
|---|---|---|
| Windows | Alt + 92 | Hold Alt and type the number on the numeric keypad. |
| HTML | \ | Paste this into HTML source. |
| Unicode | U+005C | REVERSE SOLIDUS |
Other punctuation symbols
\ lives in the Basic Latin block (U+0000-U+007F), the original ASCII set: the letters, digits and punctuation printed on a US keyboard. Within Unicode it is classified as Po, a punctuation mark.
What Backslash is used for
In mathematical notation \ is an ordinary symbol: it carries no special spacing and sits in an expression the way a letter does, standing for a thing rather than doing something to the things around it. That is the classification unicode-math gives it, and it is what decides how the symbol is set: $\backslash$ in LaTeX, in maths mode rather than in a sentence.
Unicode publishes a second list of names for \ in CLDR, the keywords its own search data offers rather than the formal name, and they are reverse, solidus and whack. Those words are what somebody looking for this character is liable to type when Backslash is not the name they know it by, and the search on the symbol lists matches them as well as the Unicode name.
What Unicode says about Backslash
The code chart points from \ to combining reverse solidus overlay (U+20E5), set minus (U+2216), mathematical falling diagonal (U+27CD) and big reverse solidus (U+29F9). These are the characters the standard thinks you might have meant instead, which makes them the ones worth checking when Backslash looks nearly right but not quite.
How Backslash behaves in software
\ takes one column in a terminal. It carries no direction of its own, so in a line that mixes English with Arabic or Hebrew it takes the direction of the text around it rather than forcing one.
Every way to write Backslash
| Form | Value |
|---|---|
| Codepoint | U+005C |
| Decimal | 92 |
| UTF-8 bytes | 5C |
| UTF-16 bytes | 00 5C |
| HTML entity | \ |
| HTML numeric | \ or \ |
| CSS | \005C |
| JavaScript | \u005C |
| Python | \u005C |
| URL-encoded | %5C |
| LaTeX, in prose | \textbackslash |
| LaTeX, in maths mode | $\backslash$ |
| SVG | 005C.svg · (SIL Open Font License) |
If \ needs escaping
\ is one byte in ASCII, in UTF-8 and in every code page in common use, so it never arrives corrupted. Its problem is the opposite one: it means something to the software reading it. In HTML it can be written \, in a URL it is %5C, and inside a CSV field, a shell command or a regular expression it has to be quoted or escaped rather than typed plainly. That is also why \ is the character people substitute when the one they wanted will not type.