Make usual programs use the alternate screen

Question

This has been annoying me for ages. Even though I use a modern terminal emulator and most CLI programs, such as less and vim, are able to use the alternate screen adequately (i.e. entering it on startup and leaving it on exit), some are reluctant to do so. Rogue programs include top, screen and dialog.

When they start, these programs clear the contents of the window (i.e. the last N lines where N is the height of the terminal window). When they exit, some (top) leave their last state visible, while others (screen) clear the screen again. In all cases, the last N lines of scrollback buffer have been overwritten.

I checked this on various machines over time, and in various terminal emulators, including xcfce4-terminal, urxvt and screen (the alternate screen of which being properly enabled, using :altscreen on). Hence I do not think it is a problem with my terminal, I rather believe it is the built-in behavior of these programs (at least unpatched, as they are distributed in Archlinux).

So my questions are:

1. Why do these programs behave like this? I guess there are good reasons for it?

2. How can I work around it? Currently, I am using dumb wrapper scripts like the one below, but maybe there is a cleaner way?

   # save this as: ~/bin/top
   
   if [ -t 1 ]; then  # only use alt screen if output is a terminal
       tput smcup  # toggle alt screen on
       /usr/bin/top "$@"
       tput rmcup  # toggle alt screen off
   else
       /usr/bin/top "$@"
   fi
   

Answer 1

Instead of trying to wrap using a shell script, we can write a short C program, which allows us to switch back to the normal screen when the program is stopped:

#define _GNU_SOURCE 1

#include <stdbool.h>
#include <stdio.h>


#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

/* Quick hack; todo: use terminfo instead */
#include <stdlib.h>
static void enter_alt_screen(void)
{
    system("tput smcup");
}
static void leave_alt_screen(void)
{
    system("tput rmcup");
}

int main(int argc, char **argv)
{
    if (argc < 2) {
        fprintf(stderr, "Usage: %s command args...", argv[0]);
        return 1;
    }

    if (!isatty(fileno(stdout))) {
        /* not a terminal; act normally */
        execvp(argv[1], argv+1);
    }

    enter_alt_screen();
    const pid_t child = fork();
    switch (child) {
    case -1:
        leave_alt_screen();
        perror("fork");
        return 1;
    case 0:
        /* child */
        execvp(argv[1], argv+1);
        leave_alt_screen();
        perror("exec");
        return 1;
    }

    int status;
    while (waitpid(child, &status, WCONTINUED) == child) {
        if (WIFSTOPPED(status)) {
            leave_alt_screen();
        } else if (WIFCONTINUED(status)) {
            enter_alt_screen();
        } else if (WIFSIGNALED(status)) {
            leave_alt_screen();
            signal(WTERMSIG(status), signal(SIGTERM, SIG_DFL));
            raise(WTERMSIG(status));
        } else if (WIFEXITED(status)) {
            leave_alt_screen();
            return WEXITSTATUS(status);
        }
    }
    return 1;
}