tput(1) -T without a tty

[Lauri Tirkkonen]

Hi,

as documented in the manual page, tput(1) no longer works without a
tty:

    Until changes made after ncurses 6.0, tput did not modify terminal
    modes.  tput now uses a similar scheme, using functions shared with
    tset (and ultimately based on the 4.4BSD tset).  If it is not able
    to open a terminal, e.g., when running in cron, tput will return an
    error.

I'm having a little trouble understanding why this is also true if using
the -T option. There's at least one (admittedly quite archaic) piece of
software that uses -T to gather information about some predefined
terminals for use in an environment where it cannot rely on ncurses:
namely, the "tigen" script during illumos build queries tput for data to
be used in the kernel debugger kmdb. See
https://github.com/illumos/illumos-gate/blob/master/usr/src/cmd/mdb/tools/scripts/tigen.sh#L32

But using ncurses tput, which requires a tty, the illumos build cannot
be run from cron. I've thrown together the following quick patch to
avoid opening a tty if -T is given; is this a reasonable use case?

diff --git a/progs/tput.c b/progs/tput.c
index 3295d18..f6e8e8f 100644
--- a/progs/tput.c
+++ b/progs/tput.c
@@ -155,7 +155,8 @@ tput_cmd(int fd, TTY * saved_settings, bool opt_x, int 
argc, char *argv[])
 
        if (is_reset) {
            reset_start(stdout, TRUE, FALSE);
-           reset_tty_settings(fd, saved_settings);
+           if (saved_settings)
+               reset_tty_settings(fd, saved_settings);
        } else {
            reset_start(stdout, FALSE, TRUE);
        }
@@ -165,13 +166,16 @@ tput_cmd(int fd, TTY * saved_settings, bool opt_x, int 
argc, char *argv[])
 #else
        (void) fd;
 #endif
-       set_control_chars(saved_settings, terasechar, intrchar, tkillchar);
-       set_conversions(saved_settings);
+       if (saved_settings) {
+           set_control_chars(saved_settings, terasechar, intrchar, tkillchar);
+           set_conversions(saved_settings);
+       }
        if (send_init_strings(fd, &oldmode)) {
            reset_flush();
        }
 
-       update_tty_settings(&oldmode, saved_settings);
+       if (saved_settings)
+           update_tty_settings(&oldmode, saved_settings);
        return 0;
     }
 
@@ -282,6 +286,7 @@ main(int argc, char **argv)
     int result = 0;
     int fd;
     TTY tty_settings;
+    TTY *settings = &tty_settings;
     bool opt_x = FALSE;                /* clear scrollback if possible */
 
     prg_name = check_aliases(_nc_rootname(argv[0]), TRUE);
@@ -296,6 +301,7 @@ main(int argc, char **argv)
        case 'T':
            use_env(FALSE);
            term = optarg;
+           settings = NULL;
            break;
        case 'V':
            puts(curses_version());
@@ -326,7 +332,10 @@ main(int argc, char **argv)
     if (term == 0 || *term == '\0')
        quit(2, "No value for $TERM and no -T specified");
 
-    fd = save_tty_settings(&tty_settings);
+    if (settings)
+       fd = save_tty_settings(settings);
+    else
+       fd = STDOUT_FILENO;
 
     if (setupterm(term, fd, &errret) != OK && errret <= 0)
        quit(3, "unknown terminal \"%s\"", term);
@@ -334,7 +343,7 @@ main(int argc, char **argv)
     if (cmdline) {
        if ((argc <= 0) && !(is_clear || is_reset || is_init))
            usage();
-       ExitProgram(tput_cmd(fd, &tty_settings, opt_x, argc, argv));
+       ExitProgram(tput_cmd(fd, settings, opt_x, argc, argv));
     }
 
     while (fgets(buf, sizeof(buf), stdin) != 0) {
@@ -355,7 +364,7 @@ main(int argc, char **argv)
        argvec[argnum] = 0;
 
        if (argnum != 0
-           && tput_cmd(fd, &tty_settings, opt_x, argnum, argvec) != 0) {
+           && tput_cmd(fd, settings, opt_x, argnum, argvec) != 0) {
            if (result == 0)
                result = 4;     /* will return value >4 */
            ++result;

-- 
Lauri Tirkkonen | lotheac @ IRCnet