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Full Discussion: until loop fails.
Top Forums Shell Programming and Scripting until loop fails. Post 302353767 by pludi on Wednesday 16th of September 2009 06:37:17 AM
Old 09-16-2009
$! captures the PID of the last process run in the background, that's correct. But that won't reset the value. Consider this: If you'd happen to start more than one background process, which one should reset $! ? What if you'd want to wait for the other process?

It's better to check the process list for the PID of the background job, and act based on that:
Code:
abc.sh &
PID=$!
while ps $PID > /dev/null
do
    echo '..\c'
    sleep 1    # So we don't hog the CPU
done

 

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SETSID(2)						     Linux Programmer's Manual							 SETSID(2)

NAME
setsid - creates a session and sets the process group ID SYNOPSIS
#include <unistd.h> pid_t setsid(void); DESCRIPTION
setsid() creates a new session if the calling process is not a process group leader. The calling process is the leader of the new session, the process group leader of the new process group, and has no controlling tty. The process group ID and session ID of the calling process are set to the PID of the calling process. The calling process will be the only process in this new process group and in this new session. RETURN VALUE
On success, the (new) session ID of the calling process is returned. On error, (pid_t) -1 is returned, and errno is set to indicate the error. ERRORS
EPERM The process group ID of any process equals the PID of the calling process. Thus, in particular, setsid() fails if the calling process is already a process group leader. CONFORMING TO
SVr4, POSIX.1-2001. NOTES
A child created via fork(2) inherits its parent's session ID. The session ID is preserved across an execve(2). A process group leader is a process with process group ID equal to its PID. In order to be sure that setsid() will succeed, fork(2) and _exit(2), and have the child do setsid(). SEE ALSO
getsid(2), setpgid(2), setpgrp(2), tcgetsid(3), credentials(7) COLOPHON
This page is part of release 3.25 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. Linux 2008-12-03 SETSID(2)
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