The shell updates the terminal output information in place

Foreword

Sometimes we need to update the same line of output information instead of outputting a new line, such as a progress display.Two implementation methods:

Output the backspace character \b, clear the input character on the line
Output the carriage return character \r, and then overwrite the output character
For the first implementation, how many characters have been outputted on the line, it needs to be output exactlyThe same amount of \b to prevent some terminal implementations from eating the carriage return on the previous line as well.You can use the return value of printf() to get the number of characters printed.

For the second implementation, the number of new characters output must be at least as many as already output to completely overwrite the previous output.

I prefer the second implementation, as long as the number of characters output in each line is the same (the number of output characters of the parameter specified by printf()), the implementation is more concise and maintainable.

This article gives implementation examples of C language and Shell respectively.

C language implementation

#include #include int main(void){int i;for (i = 0; i < 100; i++) {printf("\rprogress: %3d %%", i);fflush(stdout);sleep(1);}printf("\n");return 0;}

It is important to note that the terminal device is a line buffer device, that is, unless a newline character \n is output or the buffer is full, printf() will not have any output; so here you need to use fflush(stdout) to clear the standard outputbuffer to immediately output the buffer contents.

Shell implementation

#!/bin/bashfor i in {1..100}doprintf "\rprocess %3d %%" $isleep 1done# print a new lineecho

The printf command line program can be used in scripts.