Warning: you know how they say "there's not such thing as a stupid question"? Well, this one is, or, I suspect it's really minor, but wth, why not ask. Search engines didn't bring me anything remotely useful, though that could be bad searchterm-fu.
I recently downloaded sqlite3 onto Ubuntu 10 to start learning SQL commands. I un-tar'd 3.7.12.01 and make installed.
After creating a test.db with create table test (id) I decided to see what I'd get if I cat it. Just because.
The result is an EOT character (u+0004) which is sitting right over my prompt. Illustrated screenshot: http://imgur.com/omfMa
I realise this is not the type of file you would use cat on. I only want to know, before I go further,
does the strange placement of this character signal any future issues when actually playing around with SQL, or some issue with newlines, or fonts (this is monofur set at a high font size) or similar?
I've never seen a result character placed directly over my prompt before.
The character is placed over your prompt, because it is a double-width character, and terminals in general are not good at handling double-width characters. It does not mean anything.
There are some control codes which can do very funny things with your terminal, such as changing colors, fonts etc.
But none of them do really harm - you should be able to reset your terminal to a healthy state, or close it and open a new one.
Related
I am looking to implement a remote client in golang which connects to Linux through nc and starts bash. So I need to tell bash what features I can parse from the stdout that it sends to me, and how I am going to send keycodes and other stuff to its stdin, so that it could parse them too.
This is done with TERM=something environment variable, which I need to set to some value. If I don't set it, then various programs start to complain:
$ mc
The TERM environment variable is unset!
I found that I can set TERM to dumb to say that my client is really limited. And still it seems that I am missing something.
$ export TERM=dumb
$ mc
Your terminal lacks the ability to clear the screen or position the cursor.
From here it looks like dumb terminal don't have these two abilities, but what abilities it is still expected to have? Is there a specification or some de-facto standard about it?
Going to the source can help. The terminal database has comments. Here is a slice from that:
#### Specials
#
# Special "terminals". These are used to label tty lines when you don't
# know what kind of terminal is on it. The characteristics of an unknown
# terminal are the lowest common denominator - they look about like a ti 700.
#
dumb|80-column dumb tty,
am,
cols#80,
bel=^G, cr=^M, cud1=^J, ind=^J,
unknown|unknown terminal type,
gn, use=dumb,
The "dumb" and "unknown" terminal types are assumed, but rarely used:
"dumb" has automargins (text "wraps" at the right margin), is assumed to have 80 columns, and an ASCII BEL and carriage return. For lack of something better, cud1 (cursor down) is an ASCII line-feed. The ind (index) value is the same, implying that text scrolls up when you reach the bottom of the screen.
There is no cursor-addressing (cup) nor alternates (such as moving along a row or column arbitrarily).
"unknown" adds the "generic" flag, which marks it as unsuitable for use by curses applications. Think of it as a printer.
As for minimum requirements, that actually depends upon the individual application. ncurses can manage to move around the screen without actually having cup. It works with a half-dozen strategies. If you read the source for mvcur, you can get an idea of what it needs.
However, applications such as mc do not simply rely upon ncurses to decide if it works, since (in this case) it may link with slang (which doesn't check that closely). So mc does its own checks, which may add restrictions.
In practice, unless you choose a limited terminal description such as "dumb", most of the terminals you are likely to encounter will work.
Further reading:
terminfo - terminal capability data base
curses interfaces to terminfo database (including mvcur)
ncurses/tty/lib_mvcur.c
Your best source of information will be the terminfo entry, easily viewed with the infocmp tool:
infocmp dumb
# Reconstructed via infocmp from file: /lib/terminfo/d/dumb
dumb|80-column dumb tty,
am,
cols#80,
bel=^G, cr=^M, cud1=^J, ind=^J,
which makes it pretty clear that the dumb terminal is quite limited ...
I'm not sure if this question is appropriate here but I have nowhere else to ask. I recently started to typeset some 'mathsy' stuff using Latex and it became a hobby for me. I've been using TeXnicCenter for this, but feeling that I've got familiar with Latex language, I decieded to improve 'efficiency' of typesetting by changing the editor.
So I decided to use Vim (latest version, 7.4) with Suite-Latex. I've just installed Vim and Suite-Latex, following exactly what was instructed here. I made every necessary changes mentioned here, and it seemed to me that installation was successful (I got what was expected on Step 4)
Then I started to work through this tutorial and everything went fine until this section.
When I press F9 for autoreference, I see that Vim is working on something for split seconds and red error message refering to "can't find [some file name]" in my user/appdata/local/temp directory. The "file name" changes every time I do this (so its kind of temporary file as its directory suggests?). And then it produces a new window with title __ OUTLINE __ where 2 empty lines are showing up.
If I press n (in the new window described above) error message saying "E486: Pattern not found: rf" pops up and pressing j results in going down one row. If I press enter key, message ":call Tex_FinishOutlineCompletion()" pops up.
More frustratingly, if I try to compile a file by entering command \ll, a new window pops up where there are two lines saying:
1.ll I can't find file `newfile.tex'. newfile.tex
2.ll Emergency stop
and below these is a message saying
[Quickfix list]: latex -interaction=nonstopmode -file-line-error-style newfile.tex
So I thought it maybe is something to do with VIM not being able to find files in my computer (so something wrong with grep?), and I tried to resolve it by downloading a software called "cygwin" on which developers said their tests were successful, but it changed nothing.
But I think the two problems are related.
As it is, I am completely newbie in this type of editing environment (or any kind of programming) but I really would like to learn some Vim seeing how efficient it is in typesetting etc. Sorry for not being a pro at typing codes here. Thanks for reading!
I believe you need a latex compiler---I've had this issue and well, one thing that's left out of the conversation a lot is the compiler (pdflatex, latexmk, etc). As of now, you should download a compiler since vim-latex (latex-suite) doesn't actually come with a compiler (that I know of) and it's just a plug in with some cool stuff in it, but not what you need to make a file.pdf out of your file.tex.
It happened to me before. I found out that this problem may happen when you have special characters (such as white space and other symbols) in your file name or folder path. Try again with file name and path only in English letters.
I have a Tcl/Tk expect script, and log information is logged to external log file.
I can execute it on Linux server successfully without any wrong, and the log file do not have any weird ^H. But when the script is called by Jenkins job, run on the same Linux server. the log file will have a lot of ^H, And the expect will timeout.
What the possible reason could be?
The ^H is actually the backspace character, U+000008, and it is used in terminals (and terminal emulators) to move the current character insertion position one place to the left. This is used in turn to simulate various kinds of effects, such as making a character bold (by double-striking) or giving it an underline (by putting a _ on the same cell). Think like it's going to a traditional teletype, which prints things into the same position twice. It's definitely a hang-over from
the old days.
It seems that Jenkins (or maybe whatever it is calling, quite possibly maven though definitely not necessarily!) is using that device to back up over what it has written so it can write a new value there instead, probably for something like a simple download progress meter. Things that are writing to what they think is a terminal sometimes do this. You'll just have to cope. A \b in your Expect regular expressions will match it, though it is possibly unwise to do so, as whatever is being overwritten is transient info. If the characters are being written to a file, the col program (part of the nroff/groff suite) can be used to strip them; that might be easier.
Be aware that there are other ways that software can achieve the same effect, such as writing just a carriage return (which puts the cursor back at the start of the current line).
I can scroll trough bash output using shift+pgup/pgdown.
But lets say, some command outputted lot of text, I have to pageup few times to go to beginning of output of this command.
Can I just simply do this by some shortcut? Something that simply allows me to scroll between previous commands (not history!), seeing their output.
You could try piping the output into less:
someCommand | less
less will allow you to search and scroll through the output text pretty easily.
once in less you can just type % to jump back to the top of the page. Essentially that means jump to 0% of the page. There are also a bunch of extra commands on the page I linked to above.
Another option is to use screen and use backward search (beware: read the Overview first, especially the part about the C-a prefix) to e.g. search for some specific characters in your prompt (like your username).
The scroll back history in Unix shells is a shell specific functionality, meaning that it is up to the specific shell (xterm, rxvt, text console, etc) to handle it. The functionality you request would require the shell to identify the individual program runs, to know where to scroll to. Scanning text is not technically hard per se, but as prompts and command display can differ due to user settings it can be hard to make it work generally good. Some communication between the shell and the terminal could make it better.
There sure are some nice fancy terminal programs doing things like this, to for example show syntax help when writing commands, but for your case I agree with previous answer, that piping commands to less is a good way to isolate the output. It might be a bit cumbersome first, as it requires you to think about it first, and not just go back in history, but if you learn the shell better and learn to use the command history it will probably work fine. I recommend you to, if you haven't already. What I mean is ctrl-r etc. More described for example here:
http://www.catonmat.net/blog/the-definitive-guide-to-bash-command-line-history/
Next week I am getting an exam on using basic commands and shell scripting using terminal in Ubuntu. Please help me out with two quick questions:
-Does a practice environment for the Ubuntu terminal exist? I don't want to dual boot with Linux, so I want to find somewhere I could practice using some basic terminal commands as Cygwin seems to be quite different from the ubuntu terminal.
-What does the col command in Linux do? The manual page is here: Link, but I find that hard to understand, and since it doesn't work in Cygwin, it's hard to interpret! Also, why would one use man piped to col -b -x?
Thank you very much and sorry for the probably silly questions!
You can use the Ubuntu LiveCD boot (boots up an Ubuntu system without actually installing it) and experiment with the Ubuntu terminal shell. Its actually the same CD as the standard Ubuntu installtion CD... you just chose "Try Ubuntu" instead of "Install Ubuntu" once it boots up:
https://help.ubuntu.com/community/LiveCD
col is program to filter out reverse-linefeeds (i.e. the backspace character) from text input. In the olden days of line printers, a common method to achieve boldface print was to print a character, then print a backspace character, then print the character again. This would make the printer strike the character twice in the same place. Some programs would emit text files formatted in this way (man is one such program)-- but if you then tried to display that text file to your terminal screen, you might end up seeing something like this: "here is b^Hbo^Hol^Hld^Hd text".
col -b simply filters text input to strip out those extra backspace and double-strike characters. The -x option converts tab characters to space characters, which might be useful if the output was formatted for a device with a particular tab width, but then displayed on a different device.
man pages often have the backspace/double-strike text embedded in them, so man piped into col was often useful.
Nowadays, most terminal emulators actually know how to handle the backspace/double-strike, so col doesn't get used as much.
Far better (easier to use, install, maintain, etc.) than Cygwin, and perhaps less resource-using than a virtual machine, is http://andlinux.org . That will give you a shell on your Windows desktop, and you can play with the col command to better understand it.
Win-bash is essentially the same shell as linux, but on windows. You can use this to experiment outside Linux but I'm not sure how effective it is.
Other options are virtual machines, and if you don't mind a reboot, you can install ubuntu with wubi which means it can be deleted from windows' add/remove programs when you are done with it. (Or just use the live disc)
Col has very limited use for most people, it only affects programs that write lines asynchronously as opposed to line by line...