I tried less command to view files in a zip file and to my surprise when I was done with the output, all my previous screen data was still present (which is not the case if i use more command for viewing a file content).
how does less command able to do this ?
Please refer the below images for more information..
before running the less command below is the terminal content,
After running the less command below is the terminal content,
How is less able to retain the terminal information unlike other commands like cat or more or zcat ?!
Any reference on this would also be of great help !
Thanks in advance..
Related
im trying to write a bash script and i want it to be able to divide the screen in 2 sections and show a message on one of them and the output of a command in the other without having to split the terminal window just like htop or nvtop. I looked it up everywhere and im not getting a place to start.
top segment:
echo "now we are executing x command"
bottom segment:
sudo apt update -y
#above command's output
blablablablabla updating this and that
updated
your repositories work
blablablablabla
image for reference :
htop divisory lines
i looked everywhere on google and couldnt get a starting point, I also search for a way to leave a static header on the terminal with the command output refreshing underneat but still no luck finding something useful
Your reference image is for bashtop
That github project code would likely give you hints on how to proceed for what you want.
I just ran a script on a server that generates a lot of output on the command window.
However, now, after running it for roughly 4 hours I want to check all the output, but the beginning of the output has already disappeared from the terminal window. When I scroll up, it is not there anymore.
Is there any way to access this? It needs to be via commands in the terminal because I'm running it on a server.
Thanks.
Best way is to redirect the output to a file & open the file to check for all the output.
You can also redirect the script by running it in background & saving the output to a file. Do let me know what type of command you are running for which I can give you the exact command. :)
if it's a real terminal and not a virtual terminal
you need to recompile your kernel and increase the buffer size of your terminal.
in the .config file of your kernel the parameter you need to increase is
CONFIG_VGACON_SOFT_SCROLLBACK_SIZE
Actually, redirecting I/O interferes with many programs (for instance, changing the output from a tty to a plain file). Use the script program to capture all output from programs run in a shell, with minimal interference.
so, I'm solid on linux basics, and have never written a shell script. But there is something I would like to get, or do.
Would it be possible to have linux log ALL COMMANDS I EVER TYPE in a single file? I.e., every ls -l and cd /this/folder etc., but also the install records I have done and more.
If this file exists great. If there is a persistent file created for EACH session and user, then maybe I can write a script to conjoin the lines. Or, what other options are available?
I'd like the file to have 3 columns, user executing, datetime executed, and copy of the command string. Some kind of results or error if returned would be great. MANY THANKS from a guy who is amazed what Linux is capable of doing!
Assuming you're running bash, look at your ~/.bash_history file.
I am developing a Qt application in Linux. I wanted to pass Linux commands to a terminal. That worked but now i also want to get a response from the terminal for this specific command.
For example,
ls -a
As you know this command lists the directories and files of the current working directory. I now want to pass the returned values from the ls call to my application. What is a correct way to do this?
QProcess is the qt class that will let you spawn a process and read the result. There's an example of usage for reading the result of a command on that page.
popen() ， api of linux systerm , return FILE * that you can read it like a file descriptor， may help youp erhaps。
Parsing ls(1) output is dangerous -- make a few files with funny names in a directory and test it out:
touch "one file"
touch "`printf "\x0a\x0a\x0ahello\x0a world"`"
That creates two files in the current working directory. I expect your attempts to parse ls(1) output won't work. This might be alright if you're showing the results to a human, (though a human will be immensely confused if a filename includes output that looks just like ls(1) output!) but if you're trying to present something like an explorer.exe or Finder.app representation of files in the filesystem, this is horribly broken.
Instead, use opendir(3), readdir(3), and closedir(3) to read directory entries yourself. This will be safer, more portable, and (as a side benefit) slightly better performing.
When you scroll up, say to see a log, the first portion of it will not be visible since the terminal only supports a limited no. of lines. So if you want to scroll up and be able to see everything, at least a few pages up, how do you do it?
Use Shift+Page Up and Shift+Page Down.
Piping the output to a pager like the following is a better choice:
command | less
command | more
You can enable unlimited scroll back (or a huge amount if you want).
To do this, go to
File → Profile preferences → Scrolling [tab]
Then, check Unlimited, or set the number of lines desired. And of course, it only applies to the next typed lines.
Some tricks I use-
some terminal applications (gnome-terminal) allow you to increase the scroll-back buffer size
pipe output to a file:
command > file.log
pipe your command to less:
command | less
tail log and pipe to grep to reduce output
tail -f example.log | grep 'search text'
An alternative to screen is using tee to copy all output to a file while still printing it on the terminal:
yourcommand | tee output.txt
Try using the screen command, and set its scrollback buffer to a larger size.
screen has many other benefits and wonderful features.
If all you're doing is looking at a log, you could alternately use a pager such as less
If you want to scroll line by line, you can use
Control+Shift+Up/Down Arrows.
If you are using gnome-term (the default), then you can change your settings. Either set the no. of lines to unlimited, or to a much larger buffer size than the default.
Essentially seconding to #zerick's solution but if you're on gnome-terminal you can modify its config. See this.
If you are in tmux (can create multiple terminal sessions in a single terminal session, highly recommended), you can easily use your normal navigation keys to scroll around after you do Ctrl-b then [, for more details let's take a look at: How do I scroll in tmux?
None of these answer the original question. All answers are how to make new terminal windows (or current one) start behaving a certain way. The question is about how to see whats already scrolled away.
To answer this, each terminal session should have it's own "history" file (not to be confused with what command history is) containing all the stuff that relates to stdin/stdout displayed. I could be wrong but this may be different depending on the terminal emulator you use. Some just trash it when you close the window/ end the session.
I am trying to get this figured out myself so here is the more direct answer in a different thread.
https://unix.stackexchange.com/questions/145050/what-exactly-is-scrollback-and-scrollback-buffer
From what this tells me, I suspect best advice you can get is, for whatever terminal emulator you use, look for where it stores the scrollback buffer and that might be your only hope. It's what I am going to try right now. (and that is IF the session is currently still open, not closed terminal windows)