1 Digraphs
2 ========
3 :author: Aaron Ball
4 :email: nullspoon@iohq.net
5
6 Wikipedia defines digraphs (and trigraphs) as
7
8 [quote, Wikipedia, 'http://en.wikipedia.org/wiki/Digraph_%28computing%29[Digraphs and trigraphs]']
9 ____
10 sequences of two and three characters
11 respectively, appearing in source code, which a programming language
12 specification requires an implementation of that language to treat as if they
13 were one other character.
14 ____
15
16
17 If you've spent much time in Unix, you have likely seen their character
18 representations on a rare occasion. Usually they begin with a ^ followed by
19 some key code. Note though that I said "spent much time in _Unix_ though. This
20 is because Linux doesn't _usually_ (with some exceptions) have problems with
21 digraphs. When I say Unix though, I am referring to the really old ones that
22 claim to be up-to-date like AIX, Solaris, and HPUX.
23
24
25 [[what-do-digraphs-have-to-do-with-old-unix]]
26 == What do digraphs have to do with old Unix?
27
28 Digraphs are actually used every time you use a Unix/Linux box from the
29 command line. There's this realy nifty thing called *stty* that flies
30 under the radar most if not all of the time on newer systems. I don't
31 know of a single Linux distro that doesn't set stty for you. The reason
32 it flies under the radar so often is because it's something that's been
33 standardized for so long that it is all but set in stone (as far as I
34 know). It's also super handy to have set, and super infuriating to not
35 have set.
36
37
38 [[what-is-stty]]
39 === What is stty?
40
41 Well, technically STTY is an acronym for "**S**et **TTY**". That's tons of help
42 though. What's TTY? It turns out that
43 http://en.wikipedia.org/wiki/Tty_%28Unix%29[TTY] is an acronym for
44 **T**ele**TY**pewriter. Combining all that goodness, we have **S**et
45 **T**ele**TY**pewriter.
46
47 Now, all this is great, but really, what does this have to do with anything? It
48 turns out that while we nearly never need to directly deal with it, we actually
49 use it all the time. Here's a short list of a few things we use it for in
50 *nix...
51
52 * Backspace
53 * Scrolling with a mouse in a terminal
54 * Ctrl+C (sigterm)
55 * Ctrl+D (logout/eof)
56 * All arrow keys, both horizontal and vertical
57
58 I mentioned earlier that stty is set by default on nearly all modern Linux and
59 Unix distributions with the exception of old Unix distributions such as AIX,
60 Solaris, and HPUX. I posed this question to a few AIX admins I know and all of
61 them told me that IBM doesn't set stty for you by default because it's more
62 customizable than Linux, therefore better. I have my own very charged opinion
63 as to why they don't set a default, but I will leave that out of this post.
64
65
66 [[what-does-stty-look-like]]
67 == What does stty look like?
68
69 Where I work, management is endeavoring to make their Linux environment as much
70 like AIX as possible. One step in that process is to merge the .profile
71 configurations. Since Linux doesn't have stty set in .profile because the
72 system has a default, AIX using a Linux .profile doesn't support the
73 afforementioned list of modern keyboard keys (backspace? really? no). Imagine
74 how infuriating command line can get without arrow keys for cursor movement, a
75 backspace to correct your mistakes, and Ctrl+C to clear your line or stop your
76 process. The only option we have here is to re-set the Linux stty so when the
77 profile is sent over to an AIX system, it also has stty set on login. Here's my
78 attempt at porting my Arch Linux stty to aix.
79
80 ----
81 stty erase ^? kill ^U intr ^C eof ^D quit ^\ start ^Q stop ^S susp ^Z rprnt ^R werase ^W lnext ^V flush ^O time 0 -parenb -parodd cs8 -hupcl -cstopb cread -clocal -ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon -ixoff -iuclc -ixany -imaxbel -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0
82 ----
83
84
85 [[what-does-all-that-do]]
86 == What does all that do?
87
88 I really only want to cover a few things in that list because they are the most
89 frequently used and caused me trouble when I was trying to set this up.
90
91 Each of those items up there starting with a
92 https://en.wikipedia.org/wiki/Caret#Circumflex_accent[\^ (Circumflex Accent)]
93 represents a control key combination. For instance, +eof \^D+ will send the
94 logout signal upon pressing Ctrl+D. The problem here is that those "circumflex
95 accents" aren't caret characters. A circumflex accent is its own character. How
96 do we do these in vi/vim? You need another control key combination to tell
97 vi/vim that you are going to be pressing a control key combination of course!
98
99 To do, for instance, the Ctrl+D sequence in vim, go into insert mode and type
100 +Ctrl+v Ctrl+d+ (the d is not capitalized) and you should see +\^d+ show up.
101
102 I did have two problems with this method though: \^S and \^Q. It turns out that
103 those aren't Ctrl+S and Ctrl+Q. Since I didn't know those, I elected to use the
104 actual digraph instead of the character version to set them. To do this, go
105 into insert mode again and hit +Ctrl\+k+ and type the digraph. In the
106 case of \^Q and \^S, these are D1 and D3, respectively.
107
108
109 Category:Linux
110 Category:Vim
111 Category:Unix
112
113
114 // vim: set syntax=asciidoc:
|
