utmpdup: Ensure flushing when using follow flag

The following usages of utmpdump result in no output being flushed to the specified file because the default output buffering is fully buffered:

$ utmpdump --follow --output myOutputFile /var/log/utmp
$ utmpdump --follow /var/log/utmp > myOutputFile

This change configures line buffering for these scenarios so that output will be flushed after each log event.

Signed-off-by: Andrew Shapiro <anshapiro@gmail.com>

diff --git a/login-utils/utmpdump.c b/login-utils/utmpdump.c
index 5ccae8655c5b57befb29744d1c17953455046dcb..b9a92b5f6766154ea8b938706176ecc87f7786c0 100644 (file)
--- a/login-utils/utmpdump.c
+++ b/login-utils/utmpdump.c
@@ -367,6 +367,10 @@ int main(int argc, char **argv)
        if (!out)
                out = stdout;
 
+       if (follow && (out != stdout || !isatty(STDOUT_FILENO))) {
+               setvbuf(out, NULL, _IOLBF, 0);
+       }
+
        if (optind < argc) {
                filename = argv[optind];
                in = fopen(filename, "r");