I'm trying to write a command that writes many lines of output, then rewinds to the beginning to overwrite them in sequence with more information. To do this, I count the number of lines, then move that many lines up with ANSI escape codes, then start outputting again. This works great if the many lines of output fit in the window I have open, but if there are too many lines, the cursor only ends up moving to the top visible line. How can I always go back to the beginning of the output, regardless of the window size?
One simpler option may be to use a library to do it instead of doing all the heavy lifting and calculations yourself have a look at something like BashSimpleCurses this would allow you to use the update function easily.
Related
When I am writing code in nano, the cursor bugs after some time. The cursor moves further to the right than the actual position. This makes it really difficult to debug when writing long lines.
By the way, I am using zsh on a mac, but I had the same problem with bash. It is also not specific for any programming language or file type, but happens always when I use nano.
Here are two images to illustrate the problem:
According to the cursor, hitting del should delete d, but it actually deletes n. However, when I go at the beginning of the line:
hitting del correctly deletes u.
Can anyone help me out here?
My program constantly outputs text to the terminal. I need the user input line to always stay below this output; if the user types something, it shouldn't jump over the output.
Is there any Ruby library that can provide this functionality?
There could not be any ruby library providing this functionality since none of the known terminals support splitting the areas inside themselves.
This is the terminal issue: they are not capable of dividing their internal window into two parts.
What you can do, though, it to use two different shells for input and for output with IO#popen.
i don't understand why sometimes the CUB sequence is allowed to continue through the previous line and sometimes not. the documentation tells it's not but in real situation...
http://vt100.net/docs/vt100-ug/chapter3.html#CUB
for exemple i have a screen filled with spaces on 80 columns and 24 lines.
i am at position line 3, column 4 which can be set with escape sequence : \033[3;4H
i move the cursor on the left 10 times with sequence \033[10D
wich will put me at position : line 2 column 76
so it worked ?!!
and sometimes it doesn't
please save me ! :)
I can reduce the situation but this is where i saw it :
I'm writing a vt* emulator and everithing works fine. i can launch emacs/vim and others but then i launched vttest in putty with the "script" command to record every typed characters and sequences. like so :
# script test
Script started, file is test
# vttest
...
when i do "cat test" in putty for exemple, it replays everythings like i did. when i play it with my emulator i am able to parse and to analyse every escape sequence they provide, but the display is not the same.
The wording on VT100.net is fairly clear:
If an attempt is made to move the cursor to the left of the left margin,
the cursor stops at the left margin.
In a recent discussion, someone pointed out that PuTTY honors a (non-VT100) capability bw, which quoting from ncurses' terminfo manual:
auto_left_margin bw bw cub1 wraps from col‐
umn 0 to last column
PuTTY's behavior for wrapping at the margins differs from VT100s, as you have seen. ncurses has a terminal entry named "putty", simply because PuTTY differs from all of the other terminals enough to make using a nuisance otherwise.
Looked around with numerous search strings but can't find anything quite like this:
I'm writing a custom log parser (ala analog or webalizer except not for webserver) and I want to be able to skip the hard work for the lines that have already been parsed. I have thought about using a history file like webalizer but have no idea how it actually works internally and my C is pretty poor.
I've considered hashing each line and writing the hashes out, then parsing the history file for their presence but I think this will perform poorly.
The only other method I can think of is storing the line number of the last parse and skipping until that number is reached the next time round. What happens when the log is rotated I am not sure.
Any other ideas would be appreciated. I will be writing the parser in ruby but tips in a similar language will help as well.
The solutions I can think of right now are bound to be brittle.
Even if you store the line number and later realize it would be past the length of the current file, what happens if old lines have been trimmed? You would start reading (well) after the last position.
If, on the other hand, you are sure your log files won't be tampered with and they will only be rotated, I only see two ways of doing what you want, and I'm not sure the second is applicable to you.
Anyway, here goes.
First solution
You store the last line you parsed along with a timestamp. At the next run, you consider all the rotated log files sorting them by their last modified date, figure out which one you read last time, and start reading from there.
I didn't think this through, there might be funny corner cases you will need to handle.
Second solution
You create a background script that continuously watches the log file. A quick search on Google turned out this gem, but I'm not sure if that's even an option for you. Even then, you might want to integrate this solution with the previous one just in case your daemon will get interrupted (because that's clearly bound to happen at some point).
As you read the file and parse the lines keep track of the byte count. Save that. On next read, try to seek to that byte offset in the file. If the file is smaller than the byte count, it's a new file so start at the beginning.
I have a tcl script which takes a few minutes to run (the execution time varies based on different configurations).
I want the users to have some kind of an idea of whether it's still executing and how long it would take to complete while the script executes.
Some of the ideas I've had so far:
1) Indicate it using ... which keep increasing with each internal command run or so. But again it doesn't really give a sense of how much more to go for a first time user.
2) Use the revolving slash which I've seen used many places.
3) Have an actual percentage completed output on screen. No idea if this is viable or how to go about it.
Does anyone have any ideas on what could be done so that users of the script understand what's going on and how to do this?
Also if I'm implementing it using ... , how do I get them to print the . on the same line each time. If I use puts to do this in the tcl script the . just gets printed on the next line.
And for the revolving slash, I would need to replace something which was already printed on screen. How can I do this with tcl?
First off, the reason you were having problems printing dots was that Tcl was buffering its output, waiting for a new line. That's often a useful behavior (often enough that it's the default) but it isn't wanted in this case so you turn it off with:
fconfigure stdout -buffering none
(The other buffering options are line and full, which offer progressively higher levels of buffering for improved performance but reduced responsiveness.)
Alternatively, do flush stdout after printing a dot. (Or print the dots to stderr, which is unbuffered by default due to mainly being for error messages.)
Doing a spinner isn't much harder than printing dots. The key trick is to use a carriage return (a non-printable character sometimes visualized as ^M) to move the cursor position back to the start of the line. It's nice to factor the spinner code out into a little procedure:
proc spinner {} {
global spinnerIdx
if {[incr spinnerIdx] > 3} {
set spinnerIdx 0
}
set spinnerChars {/ - \\ |}
puts -nonewline "\r[lindex $spinnerChars $spinnerIdx]"
flush stdout
}
Then all you need to do is call spinner regularly. Easy! (Also, print something over the spinner once you've finished; just do puts "\r$theOrdinaryMessage".)
Going all the way to an actual progress meter is nice, and it builds on these techniques, but it requires that you work out how much processing there is to do and so on. A spinner is much easier to implement! (Especially if you've not yet nailed down how much work there is to do.)
The standard output stream is initially line buffered, so you won't see new output until you write a newline character, call flush or close it (which is automatically done when your script exits). You could turn this buffering off with...
fconfigure stdout -buffering none
...but diagnostics, errors, messages, progress etc should really be written to the stderr stream instead. It has buffering set to none by default so you won't need fconfigure.