2013-03-15 21:21


  • stdout

I want to output to stdout and have the output "overwrite" the previous output.

For example; if I output On 1/10, I want the next output On 2/10 to overwrite On 1/10. How can I do this?

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  • drmlxgmqn18198265 drmlxgmqn18198265 8年前

    stdout is a stream (io.Writer). You cannot modify what was already written to it. What can be changed is how that stream's represented in case it is printed to a terminal. Note that there's no good reason to assume this scenario. For example, a user could redirect stdout to a pipe or to a file at will.

    So the proper approach is to first check:

    • if the stdout is going to a terminal
    • what is that terminal's procedure to overwrite a line/screen

    Both of the above are out of this question's scope, but let's assume that a terminal is our device. Then usually, printing:

    fmt.Printf("On %d/10", i)

    will overwrite the previous line in the terminal. stands for carriage return, implemented by many terminals as moving the cursor to the beginning of the current line, hence providing the "overwrite line" facility.

    As an example of "other" terminal with a differently supported 'overwriting', here is an example at the playground.

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  • dongxie548548 dongxie548548 3年前

    The solution for one string which will replace whole string

    fmt.Printf("\033[2K%d", i)

    For example, it correctly prints from 10 to 0:

    for i:= 10; i>=0; i-- {
        fmt.Printf("\033[2K%d", i)
        time.Sleep(1 * time.Second)

    which previous answers don't solve.

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  • dongxiaoguang9108 dongxiaoguang9108 6年前

    Use this solution if you want to rewrite multiple lines to the output. For instance, I made a decent Conway's "Game of Life" output using this method.

    DISCLAIMER: this only works on ANSI Terminals, and besides using fmt this isn't a Go-specific answer either.

    // put your other fmt.Printf(...) here

    Brief Explanation: this is an escape sequence which tells the ANSI terminal to move the cursor to a particular spot on the screen. The \033[ is the so-called escape sequence, and the 0;0H is the type of code telling the terminal move the cursor to row 0, column 0 of the terminal.


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