I've been searching for this for a while and didn't get a satisfactory answer for it.
I've taken this screenshot from the output of Gnu/Linux's tree command.
I want to know how to draw or print lines like these, I've tried reading the source code of the tree program but didn't understand anything.
You can do this by using the table of characters in terminfo(5) (man 5 terminfo) starting with "Line Graphics"
Glyph ACS Ascii acsc acsc Name Name Default Char Value ──────────────────────────────────────────────────────────────────── arrow pointing right ACS_RARROW > + 0x2b arrow pointing left ACS_LARROW < , 0x2c arrow pointing up ACS_UARROW ^ - 0x2d arrow pointing down ACS_DARROW v . 0x2e solid square block ACS_BLOCK # 0 0x30 diamond ACS_DIAMOND + ` 0x60 checker board (stipple) ACS_CKBOARD : a 0x61 degree symbol ACS_DEGREE \ f 0x66 plus/minus ACS_PLMINUS # g 0x67 board of squares ACS_BOARD # h 0x68 lantern symbol ACS_LANTERN # i 0x69 lower right corner ACS_LRCORNER + j 0x6a upper right corner ACS_URCORNER + k 0x6b upper left corner ACS_ULCORNER + l 0x6c lower left corner ACS_LLCORNER + m 0x6d large plus or crossover ACS_PLUS + n 0x6e scan line 1 ACS_S1 ~ o 0x6f scan line 3 ACS_S3 - p 0x70 horizontal line ACS_HLINE - q 0x71 scan line 7 ACS_S7 - r 0x72 scan line 9 ACS_S9 _ s 0x73 tee pointing right ACS_LTEE + t 0x74 tee pointing left ACS_RTEE + u 0x75 tee pointing up ACS_BTEE + v 0x76 tee pointing down ACS_TTEE + w 0x77 vertical line ACS_VLINE | x 0x78 less-than-or-equal-to ACS_LEQUAL < y 0x79 greater-than-or-equal-to ACS_GEQUAL > z 0x7a greek pi ACS_PI * { 0x7b not-equal ACS_NEQUAL ! | 0x7c UK pound sign ACS_STERLING f } 0x7d bullet ACS_BULLET o ~ 0x7e
As an example
tput smacs
printf "%s\n%s\n" 'lqqqqqk' 'mqqqqqj'
tput rmacs
Output
┌────┐
└────┘
Observations
I notice that on my system, not all the characters listed actually map as described. For example
echo '+ , - . 0 ` a f g h i j k l m n o p q r s t u v w y x z { | } ~'
tput smacs
echo '+ , - . 0 ` a f g h i j k l m n o p q r s t u v w y x z { | } ~'
tput rmacs
+ , - . 0 ` a f g h i j k l m n o p q r s t u v w y x z { | } ~
+ , - . 0 ♦ # ° ± n ↓ ┘ ┐ ┌ └ ┼ ⎺ ⎻ ─ ⎼ ⎽ ├ ┤ ┴ ┬ ≤ │ ≥ # ≠ £ ·
mosh and mine and does not support ISO 2022 character set switching, this approach does not work. See https://unix.stackexchange.com/a/289871/5132 and https://unix.stackexchange.com/a/506140/5132 . You've also discovered the pitfall of private use character sets (which is what you are using, you will find) not being standardized. Another answer's approach of emitting UTF-8 to a UTF-8 terminal emulator is the more modern, straightforward, and standard approach.
– JdeBP
Dec 31 '19 at 17:46
smacs is undefined one is (was) supposed to fall back to the column "Ascii Default". If that were applied to mosh and your own preferred terminal you would get a moderately-acceptable alternative. The real question is how to determine if UTF-8 unicode characters can be represented on the terminal device.
– Chris Davies
Jan 01 '20 at 21:11
screen session, but some digging around showed that it (and presumably other terminals) need a tput enacs first, before tput smacs will work.
These days, UTF-8 is better, though it's unclear how to know if a terminal supports it. I think the general practice is to check locale variables and see if ".UTF-8" is appended.
– mulad
Sep 08 '22 at 15:19
It requires special box-drawing characters, as commented by another user. In the terminal, it is possible to call them via the printf command. For example, to recreate the first two lines of the tree example in the question, it would look like:
printf "\x1b(0\x74\x1b(B\x1b(0\x71\x1b(B\x1b(0\x71\x1b(B info\n"
printf "\x1b(0\x78\x1b(B \x1b(0\x6d\x1b(B\x1b(0\x71\x1b(B\x1b(0\x71\x1b(B exclude\n"
For a list of the box-drawing characters, see the wikipedia page.
\x1b(0 mean or interpret to?, i've tried to print it alone and it changed how things viewed in my terminal, so what does it really mean?
– Mahmoud Farouq
Dec 31 '19 at 16:46
It just uses uni-code characters: Unicode is about 2^24 characters. It includes ASCII as its first 128 characters, then goes on to include characters from all languages (including maths) including some fictitious ones, drawing characters, emoji, and more.
You can look up the characters in the uni-code drawing characters (e.g. https://en.wikipedia.org/wiki/Box-drawing_character#Unicode ), or just copy the ones from the example.
Here are the same characters. They don't render as well on this site (probably the font). However it is the same text. If you paste back into terminal, it will look the same.
├── media
│ ├── cdrom
│ ├── other
Other answers give an alternate way to do it. I don't know the pros and cons of each. It would be nice to hear them.
I don't have tree installed, but I get the same effect from cfdisk. I pasted the output from cfdisk into od (octal dump). These symbols are just multibytes from my locale, which is LANG=en_GB.UTF-8.
This is a vertical bar with a branch to the right, followed by a horizontal continuous line: 342 224 234 342 224 200
This is a down/right corner, followed by the same horizontal: 342 224 224 342 224 200
Go to this URL:
www.ltg.ed.ac.uk/~richard/utf-8.cgi
and type in the octal 342 224 224
Or here:
www.obliquity.com/computer/html/unicode2500.html
You would need to Google for "convert Unicode Code Point to UTF-8".
Also try: echo -e '\0342\0224\0234\0342\0224\0200'
Although other answers already pointed you to box drawing characters, you should be careful using hardcoded terminal sequences in your app on your own as given in those answers. Note that there might be terminals that simply dont understand these sequences and will output some rubbish instead.
If you dont understand anything of this, either restrain from using those sequences or use a library, thats capable of handling terminal awkwardities in a uniform way, like ncurses. Those libraries also have a primitive for drawing a horizontal line (with proper fallbacks).
If you are still keen to get this done yourself and without the help of a terminal DB like libterminfo, you have the following possibilities:
