如何在 linux 终端动态显示结果？喜欢 'top' 命令

Question

我想实现一个 linux 命令，该命令从一个可变文件中读取并每隔一秒动态地在终端中显示一次。如何在 linux 终端动态显示结果？喜欢 'top' 命令？谢谢！

Answer 1

您可以像手册中描述的那样使用 watch 工具（Linux 在线手册在 man7.org 站点上）：http://man7.org/linux/man-pages/man1/watch.1.html

   watch runs command repeatedly, displaying its output and errors (the
   first screenfull).  This allows you to watch the program output
   change over time.  By default, command is run every 2 seconds and
   watch will run until interrupted.

例如：

watch -n 1 tail -n 23 file

这将每 1 秒运行命令 tail -n 23 file（显示文件 file 的最后 25 行）（watch 的选项 -n 1）。 watch 将运行命令并打印其输出，休眠几秒，然后使用终端清屏 (ANSI) command sequence. There are several implementations of watch, and the simplest is in busybox package: https://git.busybox.net/busybox/tree/procps/watch.c?h=1_17_stable

while (1) {
    /* home; clear to the end of screen */
    printf("3[H""3[J");
...
    fflush_all();
...
    system(cmd);
    sleep(period);
}

清屏有3[H和3[J顺序（fflush_all为just custom busybox variant of fflush(stdout)). Linux documents such codes in console_codes (4) man page: http://man7.org/linux/man-pages/man4/console_codes.4.html；3为ESC，ESC [是 CSI，ECMA-48 CSI sequences 部分描述了 CSI H 和 CSI J 命令：

   ECMA-48 CSI sequences

   CSI ( or ESC [ ) is followed by a sequence of parameters .. An empty or
   absent parameter is taken to be 0.  The sequence of parameters may be
   preceded by a single question mark.

   H   CUP       Move cursor to the indicated row, column (origin at 1,1).
   J   ED        Erase display (default: from cursor to end of display).

如何在 linux 终端动态显示结果？喜欢 'top' 命令

how to show result dynamically in linux terminal? like 'top' command

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