Stdout waiting for buffer fillup

Question

I am wondering how you can coax a process to output more frequently, as if it were running on a terminal or terminal window.
Currently, any process outputting on stdout on Solaris outputs normally on a terminal device such as a xterm or a telnet session. Data is output usually when a newline is made. However that same process if run outputting to a pipe or run as a remote command through something like rsh, will output only when the output buffer is filled (which seems to be about every 4K bytes). This does not occur with stderr.
If you don't believe me then try this simple example perl script:
#!/usr/bin/perl
for ($i=0; $i<=5; $i++) {
print "$i\n";
sleep 1;
If you run it from the command line you get a line printed every second. If you run it through a pipe or as a remote process, you get a 5 second wait then all the lines are printed at once. Modify the program to print to STDERR instead and this problem does not occur.
I am running into some problems with programs that run other programs. The program that is calling the other program is having to wait for the stdout 4K buffer to fill up before it receives any data.
I understand that I can modify the source code to the program that is called and force a flush (for example in C using the fflush() library call) and the process will output more frequently, however I am trying to find a solution I can use in a calling program. I do not want to modify the program called.
Does anyone know what can be done to coax a program to output more frequently? It is obvious that terminal emulator programs, such as xterm, are doing something, so there should be some sort of solution.
Any help anyone has would be greatly appreciated,
Rick Rohan

Answer 1

Figured it out. I needed a pseudo-terminal. Under Perl this is the IO::Pty module.
Rick