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Full Discussion: while loops and variables under bash
Top Forums Shell Programming and Scripting while loops and variables under bash Post 302605244 by balajesuri on Wednesday 7th of March 2012 04:00:01 AM
Old 03-07-2012
Quote:
Originally Posted by Corona688
By putting your while loop behind a pipe, you are executing it inside a subshell.
@Corona688: I too thought the same, and tried to check this by printing the pid of shell before entering while loop and inside while loop. Pid's are same. If its invoking a sub-shell it should print the pid of the sub-shell inside while loop, right?

Code:
#! /bin/bash
u=0
echo "before while, pid = $$"
ls | while read x
do
    echo "inside while, pid = $$"
    ((u++))
done

Code:
# bash --version
GNU bash, version 3.1.17(1)-release (i686-redhat-linux-gnu)
# ./test.sh
before while, pid = 6435
inside while, pid = 6435
inside while, pid = 6435
inside while, pid = 6435

Any idea what's happening here?
 

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LEARN ABOUT ULTRIX

setpgid

setpgid(3)						     Library Functions Manual							setpgid(3)

Name
       setpgid - set process group (POSIX)

Syntax
       #include <sys/types.h>
       int
       setpgid(pid, pgrp)
       pid_t pid, pgrp;

Description
       The  function is used to either join an existing process group or create a new process group within the session of the calling process (see
       Upon successful completion, the process group ID of the process that has a process ID which matches pid is set to pgrp.	If  pid  is  zero,
       then the call applies to the current process. In addition, if pgrp is zero, the process ID of the indicated process is used.

       This function is available only in the POSIX environment.

Return Values
       The  function  returns 0 when the operation is successful.  If the request fails, -1 is returned and the global variable indicates the rea-
       son.

Diagnostics
       The function fails and the process group is not altered if one of the following occurs:

       [EACCES]       The value of the pid argument matches the process ID of a child process of the calling process and  the  child  process  has
		      successfully executed an function.

       [EINVAL]       The value of the pgrp argument is less than zero or is not a supported value.

       [EPERM]	      The process indicated by the pid argument is a session leader.

		      The  value of the pid argument matches the process ID of a child process of the calling process and the child process is not
		      in the same session as the calling process.

		      The value of the pgrp argument does not match the process ID of the process indicated by the pid argument and  there  is	no
		      process with a process group ID that matches the value of the pgrp argument in the same session as the calling process.

       [ESRCH]	      The  value  of  the  pid	argument  does	not  match the process ID of the calling process of a child process of the calling
		      process.

See Also
       getpgrp(2), setsid(2)

																	setpgid(3)
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