Box-drawing characters, also known as line-drawing characters, are a form of semigraphics widely used in text user interfaces to draw various geometric frames and boxes. Box-drawing characters typically only work well with monospaced fonts. In graphical user interfaces, these characters are much less useful as it is more simple and appropriate to draw lines and rectangles directly with graphical APIs. However, they are still useful for command-line interfaces and plaintext comments within source code.
Unicode includes 128 such characters. In many Unicode fonts only the subset that is also available in the IBM PC character set (see below) will exist, due to it being defined as part of the WGL4 character set.
Official Unicode Consortium code chart (PDF)
Official Unicode Consortium code chart (PDF)
The hardware code page of the original IBM PC supplied the following box-drawing characters, in what DOS now calls code page 437. This subset of the Unicode box-drawing characters is thus far more popular and likely to be rendered correctly:
Their number is further limited to 22 on those code pages that replace the 18 "single/double hybrid" characters with other, usually alphabetic, characters (such as code page 850):
Note: The non-double characters are the "thin" (light) ones (U+2500, U+2502), not the "bold" (heavy) ones (U+2501, U+2503).
Some OEM DOS computers supported other character sets, for example the Hewlett-Packard HP 110 / HP Portable and HP 110 Plus / HP Portable Plus, where in a modified version of the character set box-drawing characters were added in reserved areas of their normal HP Roman-8 character set.
On many Unix systems and early dial-up bulletin board systems the only common standard for box-drawing characters was the VT100 alternate character set (see also: DEC Special Graphics). The escape sequence
Esc ( 0 switched the codes for lower-case ASCII letters to draw this set, and the sequence
Esc ( B switched back:
A Bash script that displays all of the semigraphic characters:
$ for i in 6a 6b 6c 6d 6e 71 74 75 76 77 78; do > printf "0x$i \x$i \x1b(0\x$i\x1b(B\n" > done 0x6a j ┘ 0x6b k ┐ 0x6c l ┌ 0x6d m └ 0x6e n ┼ 0x71 q ─ 0x74 t ├ 0x75 u ┤ 0x76 v ┴ 0x77 w ┬ 0x78 x │
On some terminals, these characters are not available at all, and the complexity of the escape sequences discouraged their use, so often only ASCII characters that approximate box-drawing characters are used, such as - (hyphen-minus), | (vertical bar), _ (underscore), = (equal sign) and + (plus sign) in a kind of ASCII art fashion.
Modern Unix terminal emulators use Unicode and thus have access to the line-drawing characters listed above.
Many microcomputers of the 1970s and 1980s had their own proprietary character sets, which also included box-drawing characters. Some of these sets, such as Commodore's PETSCII, include box-drawing symbols with no corresponding Unicode character.
The BBC Micro could utilise the Teletext 7-bit character set, which had 128 box-drawing characters, whose code points were shared with the regular alphanumeric and punctuation characters. Control characters were used to switch between regular text and box drawing.
The BBC Master and later Acorn computers have the soft font by default defined with line drawing characters.
The Amstrad CPC also has soft characters defined by default as block and line drawing characters.
Some recent embedded systems also use proprietary character sets, usually extensions to ISO 8859 character sets, which include box-drawing characters or other special symbols.
The World System Teletext (WST) uses pixel-drawing characters for some graphics. A character cell is divided in 2×3 regions, and 26 = 64 code positions are allocated for all possible combinations of "pixels". However, these characters are not included in the Unicode standard. (to do: 2020 Unicode update includes Teletext sixel characters)
On many platforms the character shape is determined programatically from the character code.
ZX Spectrum block characters: 0x80 + topright*1 + topleft*2 + bottomright*4 + bottomleft*8
Amstrad CPC block characters: 0x80 + topleft*1 + topright*2 + bottomleft*4 + bottomright*8
Amstrad CPC line characters: 0x90 + up*1 + right*2 + down*4 + left*8
BBC Master line characters: 0xA0 + down*1 + right*2 + left*4 + up*8
Teletext block characters: 0xA0 + topleft*1 + topright*2 + middleleft*4 + middleright*8 + bottomleft*16 + bottomright*64
DOS linedraw characters are not ordered in any programatic manner, and calculating a particular character shape needs to use a look-up table.
Sample diagrams made out of the standard box-drawing characters, using a monospaced font:
┌─┬┐ ╔═╦╗ ╓─╥╖ ╒═╤╕ │ ││ ║ ║║ ║ ║║ │ ││ ├─┼┤ ╠═╬╣ ╟─╫╢ ╞═╪╡ └─┴┘ ╚═╩╝ ╙─╨╜ ╘═╧╛ ┌───────────────────┐ │ ╔═══╗ Some Text │▒ │ ╚═╦═╝ in the box │▒ ╞═╤══╩══╤═══════════╡▒ │ ├──┬──┤ │▒ │ └──┴──┘ │▒ └───────────────────┘▒ ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒
|Wikimedia Commons has media related to Text mode box drawing.|
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