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Full Discussion: Getting piped input from a program that's buffering it's stdout
Top Forums Shell Programming and Scripting Getting piped input from a program that's buffering it's stdout Post 302982925 by Corona688 on Tuesday 4th of October 2016 06:05:35 PM
Old 10-04-2016
expect won't help. I've looked through l2ping.c and it prints line-buffered anyway, it's not what's holding you up.

I don't think this construct:

Code:
for X in whatever
do
   something &
done | command

...necessarily does what you think. Background commands are liable to freeze themselves when they try to write to the terminal. Make sure they have absolutely no connection to the terminal:

Code:
for X in whatever
do
   something 2>/dev/null </dev/null &
done | command

In particular, sed may be making you wait, too. Make sure you run sed -u.
 

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LEARN ABOUT DEBIAN

pty

PTY(4)							   BSD Kernel Interfaces Manual 						    PTY(4)

NAME

     pty -- BSD-style compatibility pseudo-terminal driver

SYNOPSIS

     device pty

DESCRIPTION

     The pty driver provides support for the traditional BSD naming scheme that was used for accessing pseudo-terminals.  When the device
     /dev/ptyXX is being opened, a new terminal shall be created with the pts(4) driver.  A device node for this terminal shall be created, which
     has the name /dev/ttyXX.

     New code should not try to allocate pseudo-terminals using this interface.  It is only provided for compatibility with older C libraries that
     tried to open such devices when posix_openpt(2) was being called.

FILES

     The BSD-style compatibility pseudo-terminal driver uses the following device names:

     /dev/pty[l-sL-S][0-9a-v]  Pseudo-terminal master devices.

     /dev/tty[l-sL-S][0-9a-v]  Pseudo-terminal slave devices.

DIAGNOSTICS

     None.

SEE ALSO

     posix_openpt(2), pts(4), tty(4)

HISTORY

     A pseudo-terminal driver appeared in 4.2BSD.

BUGS

     Unlike previous implementations, the master slave device nodes are destroyed when the PTY becomes unused.	A call to stat(2) on a nonexistent
     master device will already cause a new master device node to be created.  The master device can only be destroyed by opening and closing it.

     The pty driver cannot be unloaded, because it cannot determine if it is being used.

BSD
								  August 20, 2008							       BSD
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