Am 04. Feb, 2016 schwätzte der.hans so:
moin moin,
for completeness...
you made me reach to the Advanced Bash-Scripting Guide to remember the
variable name :).
Notice the values of $BASHPID in a COMMAND EXECUTION ENVIRONMENT vs in a
true subshell.
http://www.tldp.org/LDP/abs/html/internalvariables.html#BASHPIDREF
:) lufthans@anke:~$ cat fred.sh
function backGround() {
echo "Pid $1 is $$ $BASHPID $SHLVL"
sleep 3
}
function backGround_subshell() {
echo "echo Pid $1 is $$ $BASHPID $SHLVL"
sleep 3
}
echo "My pid is $$ $BASHPID $SHLVL"
backGround 1 &
echo "BPid 1 is $!"
ps -ef | grep $!
(backGround_subshell 4) &
echo "BPid 4 is $!"
ps -ef | grep $!
bash -c 'echo true subshell PID $$ $BASHPID $SHLVL; ps -ef | grep $$'
wait
echo
:) lufthans@anke:~$
:) lufthans@anke:~$ bash fred.sh anke
My pid is 27811 27811 2
BPid 1 is 27812
Pid 1 is 27811 27812 2
lufthans 27812 27811 0 21:34 pts/0 00:00:00 bash fred.sh anke
lufthans 27814 27811 0 21:34 pts/0 00:00:00 grep 27812
lufthans 27815 27812 0 21:34 pts/0 00:00:00 sleep 3
BPid 4 is 27816
echo Pid 4 is 27811 27816 2
lufthans 27816 27811 0 21:34 pts/0 00:00:00 bash fred.sh anke
lufthans 27818 27811 0 21:34 pts/0 00:00:00 grep 27816
lufthans 27819 27816 0 21:34 pts/0 00:00:00 sleep 3
true subshell PID 27820 27820 3
lufthans 27820 27811 0 21:34 pts/0 00:00:00 bash -c echo true subshell
PID $$ $BASHPID $SHLVL; ps -ef | grep $$
lufthans 27821 27820 0 21:34 pts/0 00:00:00 ps -ef
lufthans 27822 27820 0 21:34 pts/0 00:00:00 grep 27820
:) lufthans@anke:~$
ciao,
der.hans
> Am 04. Feb, 2016 schwätzte Bryan O'Neal so:
>
> moin moin,
>
> $( ) is command redirection.
>
> ( ) is a subshell, sort of.
>
> Here are some excerpts from the bash man page:
>
> ###
> (list) list is executed in a subshell environment (see COMMAND EXECU
> TION ENVIRONMENT below).
>
> COMMAND EXECUTION ENVIRONMENT
> The shell has an execution environment, which consists of the
> follow
> ing:
> .
> .
> .
> · various process IDs, including those of background
> jobs, the
> value of $$, and the value of PPID
> ###
>
> If you want a full subshell, invoke bash and create another process. Also,
> check the values of SHLVL.
>
> :) lufthans@fred:~$ cat fred.sh function backGround() {
> echo "Pid $1 is $$ $SHLVL"
> sleep 3
> }
> function backGround_subshell() {
> echo "echo Pid $1 is $$ $SHLVL"
> sleep 3
> }
> echo "My pid is $$ $SHLVL"
> backGround 1 &
> echo "BPid 1 is $!"
> ps -ef | grep $!
> (backGround_subshell 4) &
> echo "BPid 4 is $!"
> ps -ef | grep $!
> bash -c 'echo true subshell PID $$ $SHLVL; ps -ef | grep $$'
> wait
> echo
> :) lufthans@fred:~$
>
> :) lufthans@fred:~$ bash fred.sh anke
> My pid is 27695 2
> BPid 1 is 27696
> Pid 1 is 27695 2
> lufthans 27696 27695 0 21:26 pts/0 00:00:00 bash fred.sh anke
> lufthans 27698 27695 0 21:26 pts/0 00:00:00 grep 27696
> lufthans 27699 27696 0 21:26 pts/0 00:00:00 sleep 3
> BPid 4 is 27700
> echo Pid 4 is 27695 2
> lufthans 27700 27695 0 21:26 pts/0 00:00:00 bash fred.sh anke
> lufthans 27702 27695 0 21:26 pts/0 00:00:00 grep 27700
> true subshell PID 27704 3
> lufthans 27704 27695 0 21:26 pts/0 00:00:00 bash -c echo true subshell
> PID $$ $SHLVL; ps -ef | grep $$
> lufthans 27705 27704 0 21:26 pts/0 00:00:00 ps -ef
> lufthans 27706 27704 0 21:26 pts/0 00:00:00 grep 27704
>
> :) lufthans@fred:~$
>
> ciao,
>
> der.hans
>
>> Sorry for the cross post but this is not an easy question I don't think....
>>
>> Given:
>> Pid of a process is $$
>> Pid of a child process just spawned is $!
>> However a child process does not see $$ as it's pid but rather the pid of
>> it's parent... How can the child process know it's own pid?
>>
>> Example:
>> [root@mybox l]# cat backTest
>> function backGround() {
>> echo "Pid $1 is $$"
>> }
>> function backGround_subshell() {
>> echo "echo Pid $1 is $$"
>> }
>> echo "My pid is $$"
>> backGround 1 &
>> echo "BPid 1 is $!"
>> backGround 2 &
>> echo "BPid 2 is $!"
>> backGround 3 &
>> echo "BPid 3 is $!"
>> $(backGround_subshell 4) &
>> echo "BPid 4 is $!"
>> $(backGround_subshell 5) &
>> echo "BPid 5 is $!"
>> $(backGround_subshell 6) &
>> echo "BPid 6 is $!"
>> wait
>> echo
>> [root@mybox l]# bash backTest
>> My pid is 16712
>> BPid 1 is 16713
>> Pid 1 is 16712
>> BPid 2 is 16714
>> Pid 2 is 16712
>> BPid 3 is 16715
>> BPid 4 is 16716
>> BPid 5 is 16717
>> BPid 6 is 16719
>> Pid 4 is 16712
>> Pid 3 is 16712
>> Pid 6 is 16712
>> Pid 5 is 16712
>>
>
>
--
# http://www.LuftHans.com/ http://www.PhxLinux.org/
# "We should not be building surveillance technology into standards.
# Law enforcement was not supposed to be easy.
# Where it is easy, it's called a police state." -- Jeff Schiller
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