I am creating a small console app that needs a progress bar. Something like...
Conversion: 175/348 Seconds |========== | 50%
My question is, how do you erase characters already printed to the console? When I reach the 51st percentage, I have to erase this line from the console and insert a new line. In my current solution, this is what happens...
Conversion: 175/348 Seconds |========== | 50%
Conversion: 179/348 Seconds |========== | 52%
Conversion: 183/348 Seconds |========== | 54%
Conversion: 187/348 Seconds |=========== | 56%
Code I use is...
print "Conversion: $converted_seconds/$total_time Seconds $progress_bar $converted_percentage%\n";
I am doing this in Linux using PHP(only I will use the app - so please excuse the language choice). So, the solution should work on the Linux platform - but if you have a solution that's cross platform, that would be preferable.
I don't think you need to apologize for the language choice. PHP is a great language for console applications.
Try this out:
<?php
for( $i=0;$i<10;$i++){
print "$i \r";
sleep(1);
}
?>
The "\r" will overwrite the line with the new text. To make a new line you can just use "\n", but I'm guessing you already knew that.
Hope this helps! I know this works in Linux, but I don't know if it works in Windows or other operating systems.
To erase a previously printed character you have three options:
echo chr(8) . " "; echoes the back character, and will move the cursor back one place, and the space then overwrites the character. You can use chr(8) multiple times in a row to move back multiple characters.
echo "\r"; will return the cursor to the start of the current line. You can now replace the line with new text.
The third option is to set the line and column of the cursor position using ANSI escape codes, then print the replacement characters. It might not work with all terminals:
function movecursor($line, $column){
echo "\033[{$line};{$column}H";
}
\r did the trick.
For future reference, \b does not work in PHP in Linux. I was curious - so I did a couple of experiments in other languages as well(I did this in Linux - I don't know if the result will be the same in Windows/Mac)..
\b Works in...
Perl
Ruby
Tcl - with code puts -nonewline "Hello\b"
\b Doesn't work in
PHP - the code print "Hello\b"; prints out Hello\b
Python - code print "Hello\b" prints out Hello<new line> . Same result with print "Hello\b",
I'm not sure if it's the same in Linux but in Windows console apps you can print \r and the cursor will return to the first left position of the line allowing you to overwrite all the characters to the right.
You can use \b to move back a single character but since you're going to be updating your progress bar \r would be simpler to use than printing \b x number of times.
This seems to be pretty old topic but I will drop my 5 into.
for ($i; $i<_POSITION_; $i--) {
echo "\010"; //issue backspace
}
Found this on the internet some time ago, unfortunately don't remember where. So all credits goes to original author.
to erase a previously printed character, I print a backspace after it:
print "a"
print "\b"
will print nothing (actually it will print and then a backspace, but you probably won't notice it)
Related
So as I'm sure you know there's a specific operator for print() functions called end.
#as an example
print('BOB', end='-')
#would output
BOB-
So is there something like this for inputs? For example, if I wanted to have an input that would look something like this:
Input here
►
-------------------------------------------------------
And have the input at the ► and be inside the dashes using something like
x = input('Input here\n►', end='-------')
Would there be some equivalent?
EDIT:
Just to be clear, everything will be printed at the same time. The input would just be on the line marked with the ►, and the ---- would be printed below it, but at the SAME time. This means that the input would be "enclosed" by the ---.
Also, there has been a comment about curses - can you please clarify on this?
Not exactly what you want, but if the --- (or ___) can also be on the same line, you could use an input prompt with \r:
input("__________\r> ")
This means: print 10 _, then go back \r to the beginning of the line, print > overwriting the first two _, then capture the input, overwriting more _. This shows the input prompt > ________. After typing some chars: > test____. Captured input: 'test'
For more complex input forms, you should consider using curses.
When using basic console IO, once a line has been ended with a newline, it's gone and can't be edited. You can't move the cursor up to do print anything above that last line, only add on a new line below.
That means that without using a specialized "console graphics" library like curses (as tobias_k suggests), you pretty much can't do what you're asking. You can mess around a little with the contents of the last line (overwriting text you've already written there), but you can't write to any line other than the last one.
To understand why console IO works this way, you should know that very early computers didn't have screens. Instead, their console output was directly printed out one line at a time on paper. While some line printers could print several characters on the same spot (to get effects line strikethrough or underline), you couldn't unprint anything once it was on the paper. Furthermore, the paper feed only worked in one direction. Once you had sent a newline character that told the printer to advance the paper, you couldn't go back to an old line again.
I believe this would solve your problem:
print(f">>> {input()} ------")
OR
print(f"{input(">>>")} ------")
F-strings are quite useful when it comes to printing text + variables.
I'm trying to make a status indicator in Rust that prints to stdout. In other languages, I've used a function that clears the current line of stdout while leaving the others untouched. I can't seem to find a Rust equivalent. Is there one? Here's a small example of what I'm looking for
for i in 0..1000 {
stdio::print(format!("{}", i).as_slice));
stdio::clear();
}
On an ANSI terminal (almost everything except Command Prompt on Windows), \r will return the cursor to the start of the current line, allowing you to write something else on top of it (new content or whitespace to erase what you have already written).
print!("\r")
There is nothing available in the standard library to do this in a platform-neutral manner.
Utilizing the ASCII code for backspace is one option, for example:
print!("12345");
print!("{}", (8u8 as char));
This will end up outputting "1234" after the 5 is removed as a result of printing the backspace character (ascii code 8). Strangely, Rust does not recognize \b as a valid character escape.
I want to show advance % in groovy , so I want to write on the same position, which means that instead of seeing:
1%
2%
3%
...
The user will see the figures changing in the same location.
How do I do that? (I'm working on windows)
I do this frequently just using a carriage return without a line feed:
printf "%5d\r", loopval
Each time through your loop, printing will start over again at the beginning of the line.
It can get a tad messy if any other messages should print out while this is happening, especially if the other message contain newlines. But it's a cheap and dirty solution.
You can use jline that comes with Groovy:
(1..5).each {
print "Done $it of 5"
Thread.sleep( 1000 )
print jline.ANSIBuffer.ANSICodes.left( 9999 )
}
So long as your console supports ANSI escape sequences, that should work...
PS: I used 9999 because (as it says in the documentation for left)
If n is greater or equal to the current cursor column, the cursor is moved to the first column
For anyone who comes across this - I found using the following to be the best solution:
(0..100).each {
print "\r$it%"
}
println()
as Danny Y. already stated, a line feed will work, backspaces will also do the trick:
(0..100).each {
print "\b"*20+it+"%"
sleep 100
}
I once had to overwrite a multipline output - the solution I found was to
print "\r\n"*80
in order to scroll all old content out of the screen - not a nice solution, but it work on windows shell :-)
In C++ I'm trying to go back up a line to add some characters.
Here is my code so far:
cout << "\n\n\n\n\n\n\n\n\n\n\xc9\xbb\n\xc8\xbc"<<flush;
Sleep(50);
As you can see, I have 10 newline characters. In my animation, a new block will be falling from the top of the screen. But I don't know how to go back up those lines to add the characters I need. I tried \r, but that dosen't do anything and \b dosen't go up the previous line either. Also, what exactly does flush do? I've only been programming in C++ for about 2 days so I'm a newb =P.
Thanks so much!!!
Christian
If your console supports VT100 escape sequences (most do), then you can use ESC [ A, like this:
cout << "\x1b[A";
to move the cursor up one line. Repeat as necessary.
In windows you can use this example
there you will create CreateConsoleScreenBuffer()
and then are using SetConsoleCursorPosition(console_handle, dwPosition);
cout will first write to internal buffer and only output it to the screen periodically and not for every character that gets inserted. This is for performance reasons.
flush tells it to empty the buffer now and show it on screen.
You should consider a library like ncurses.
How do some programs edit whats being displayed on the terminal (to pick a random example, the program 'sl')? I'm thinking of the Linux terminal here, it may happen in other OS's too, I don't know. I've always thought once some text was displayed, it stayed there. How do you change it without redrawing the entire screen?
Depending on the terminal you send control seuqences. Common sequences are for example esc[;H to send the cursor to a specific position (e.g. on Ansi, Xterm, Linux, VT100). However, this will vary with the type or terminal the user has ... curses (in conjunction with the terminfo files) will wrap that information for you.
Many applications make use of the curses library, or some language binding to it.
For rewriting on a single line, such as updating progress information, the special character "carriage return", often specified by the escape sequence "\r", can return the cursor to the start of the current line allowing subsequent output to overwrite what was previously written there.
try this shellscript
#!/bin/bash
i=1
while [ true ]
do
echo -e -n "\r $i"
i=$((i+1))
done
the -n options prevents the newline ... and the \r does the carriage return ... you write again and again into the same line - no scroling or what so ever
If you terminate a line sent to the terminal with a carriage return ('\r') instead of a linefeed ('\n'), it will move the cursor to the beginning of the current line, allowing the program to print more text over top of what it printed before. I use this occasionally for progress messages for long tasks.
If you ever need to do more terminal editing than that, use ncurses or a variant thereof.
There are characters that can be sent to the terminal that move the cursor back. Then text can be overwritten.
There is a list here. Note the "move cursor something" lines.
NCurses is a cross-platform library that lets you draw user interfaces on smart terminals.
Corporal Touchy has answered how this is done at the lowest level. For easier development the curses library gives a higher level of control than simply sending characters to the terminal.
To build on #Corporal Touchy's answer, there are libraries available that will handle some of this functionality for you such as curses/ncurses
I agree with danio, ncurses is the way to go. Here's a good tutorial:
http://tldp.org/HOWTO/NCURSES-Programming-HOWTO/